351C where to start?

351mach1 · Oct 29, 2024

Hello all! This is my first technical question post. I just purchased a 71 Mach 1 and need advice on troubleshooting steps and where to go from here.

Quick backstory: The car is an M code with Ram Air so I am assuming the ram air was aftermarket as the wiki says the factory ram air cars are Q code. The vehicle came with basically no history so lets assume we don't know anything about its past life. The only clue I have is that at some point the factory 4 speed was swapped for a C6. The P/O claimed that it was likely they rebuilt the engine when they did the swap based on how good the engine looks. It's also possible that they just threw a different engine in when they did the swap as I have not confirmed whether the engine block number matches the vin. It is definitely a 351C 4V and has a stock split bore intake manifold. I have an in depth mechanical background specializing in diesel truck repair but have never touched a carburetor; so while I may be ignorant to how to tune a carb, I do know how to turn a wrench.

Problem: Engine runs and revs ok but when in gear, it has no power, backfires, and has a big hesitation when you hit the accelerator. None of the interior gauges work and the wiring harness is pretty hacked up. P/O claimed that a month ago they borrowed a friend's edelbrock carb to put on there (to replace the Chinese copy that was currently on there) and that it ran just fine so it just needed a new carb. I installed a new Holley 600 CFM Street Warrior Carburetor and it runs exactly the same as with the chinese carb so it would appear that there is more to the story.

Goals: I want this to be a reliable weekend driver with a good bit of get up and go. From my brief research it seems that I could easily pull 400 HP/Torque from this engine with minimal upgrades. I don't have an unlimited budget and will be trying to save on costs as much as I can but am also willing to buy high quality parts if they will last the lifetime of the car.

So far: I purchased the Holley carb and have also purchased an Edelbrock performer #2665 intake manifold. I have not installed the intake yet. I plan to install the intake and replace the ignition system and perform a tune up at the same time.

Questions:
1. What ignition system to go with? I am seeing many different recommendations on several different forums. It appears that the Ram Air will limit my choices. I like the idea of the MSD plug and play options but everything I read would make it seem that they will not fit with the ram air. How much of a difference does the ram air make? If my car didn't come stock with the ram air, should I convert it back? What distributor is recommended with the ram air? It also looks like I need to choose a distributor that is compatible with the camshaft; due to the unknown history of the engine, how do I verify the camshaft?

2. Due to the unknow history, is there a way to check the timing chain and gears without pulling the front of the engine apart? Should I just plan on doing the timing chain regardless? If I have to dig in there, should I also just do the camshaft upgrade at the same time or save it for down the road?

3. What steps should I be taking here to get this engine running correctly? My current plan is to:
-Check compression to get an understanding of general engine health
-Install edelbrock intake manifold and Holley carb (any must know advice on the intake install?)
-Install upgraded ignition system (need suggestions on what to go with)
-reset ignition timing, perform tune up (plugs and wires) and see how she runs.
-Verify healthy timing chain

Other desired upgrades: I would like to upgrade the exhaust and camshaft. Suggestions?

I am currently away from the car on a work trip so wont really be able to verify anything until I get back to town. I plan to buy the shop manuals and the 351c rebuild manuals. I did snap these photos before I left. Thank you for any and all help/advice.

giantpune · Oct 29, 2024

For 1, I went with a pertronix 3 guts inside a stock style distributor.
1b - you need to make sure the gear on the bottom of your distributor is compatible with your cam. Typically, the difference is if you have a roller or flat tappet cam. The 351C only came with flat tappet. Somebody may have put a retro-fit roller cam and lifters in it. You can pop a valve cover, look down the holes in the block at the lifter valley to see the lifters. The retrofit rollers would need to have something for alignment like dog bones. Flat tappet ones do not. You can also try watching the upper tip of the push rod. Sometimes you can see it rotating on flat tappet motors. Once you know what style cam it is, you can make sure your distributor has the correct gear.

For 2, yes. The distributor is meshed with the cam. That means you can pull off the distributor cap and watch the rotor spin as the crank shaft moves. And that means you can rotate the crank 1 direction to take out the slack, then rotate it the other way and see how much it moves before the distributor rotor starts to move. That is the amount of slop in it from something like a stretched out timing chain.

Another thing you can do is remove the fuel pump and stick a boroscope in the hole. That will give you a view of the upper and lower timing gears and the chain.

3, Be mindful of your height. Many aftermarket intakes are taller than stock. That matters when you want to run ram air, which interfaces with the underside of the hood. The cheapest edelbrock, like the performer, is pretty close to stock and does good for street cars. Thats the one I'm running. And maybe its just me, but I have a terrible track record with intake manifolds if I use the torque specs in edelbrock's instructions. They seal up, then develop a vacuum leak after a few heat cycles. Edelbrock's instructions are good. I just use the normal factory torque specs, not the ones edelbrock suggests.

4, I'm a fan of long tube headers. And I like running RV style cams. They are designed for high torque and smooth idle and used in production vehicles for 100k+ miles. They have lots of torque down low where your car spends most of its time. As you go wilder in cam shaft, you give up torque down low to gain more peak horsepower up high. You also give up smooth idling, the wilder you go.

This is my 351C v2, running the edelbrock performer intake, pertronix guts in the distributor, flat top pistons, long tube headers, and RV cam. This combo is 400ftlb, 325HP and runs on 87 octane pump gas. You can shift that to 400HP, 350 ftlb with a wilder cam, and all the power will happen higher in the power band.

Stanglover · Oct 29, 2024

I didn't read all your post (yet), but the first thing I noticed was that the intake manifold is wrong for a 71...... unless someone put an aluminum Boss 351 intake on it!! You may have a 72 motor which would be a Q code. You need to check the block and date numbers located above the starter as well as the partial VIN stamped on the back left side block just under the head. It ought to match the car's VIN. You could also pull the valve covers and look at the date codes between the springs.
71 M code has very large intake ports and won't match the 72 intake
71 M code did have ram air but optional. Mine doesn't unfortunately. However it the motor is indeed a 72, the ram air could have been added.
Sorry but that's my unqualified thoughts so far.

giantpune · Oct 29, 2024

Stanglover said:
unless someone put an aluminum Boss 351 intake on it!!

All the nuts and bolts from the lowes fastener section make me doubt that.

Half the bolts we can see in the engine look like they came from the hardware store.

Sheriff41 · Oct 29, 2024

I think your approach as listed in your #3 is sound. Don't overlook the simple stuff like fluids, belts, hoses (heating/cooling and vacuum), etc.

It's not uncommon for people to put the wrong style thermostat in 351Cs so you may want to check it while your working on the engine. https://flowkoolerwaterpumps.com/co...-balanced-sleeve-thermostat-with-bypass-plate

The symptoms you describe in your Problem paragraph may indicate retarded timing. Set your base timing to 16° and see if it helps. Also, the poicture of your distributor cap shows some chewed up boots on the plug wires. You may want to change them out with new ones.

Buy a set of ARP bolts for your intake manifold or source all your engine's external fasteners from AMK Products ( https://www.amkproducts.com/i-kits/ford-individual-fastener-kits/?year_=1971&model=Mustang&category=Engine - 351C ).

I run the same Edelbrock dual plane intake you bought and it works well with my ram air.

The 600 cfm Holley is a bit on the small side for a 351C 4V. It should run okay but you'll be giving up some performance.

@giantpune made a good recommendation of the Pertronix ignition. I prefer retrofitting a Ford Duraspark 1 ignition. If you use the regular point distributor cap you'll have no clearance issues with the ram air air cleaner. The procedure for the Duraspark would be straightforward for someone with your mechanical ability. It's described in the Ignition System Improvement section of https://pantera.infopop.cc/topic/sticky-3-351c-basics-and-performance-tuning .

If you decide to change the cam, talk with some of the custom cam providers, e.g., Brent Lykins https://lykinsmotorsports.com/ so you can match your cam with the other mods on your car. You want to build it as a system rather than just throwing parts together.

Ceramic coated Hooker Competition headers have performed well for me and have held up for over 20 years.

Keep us posted on your progress with your build!

Steve McMahan · Oct 29, 2024

Just a thought since your car has amnesia, it’s possible your symptoms point to a contamination fuel tank. I know you changed the carb, but did you trace back to the pump and the tank to verify clear fuel flow? Since the PO didn’t give you the straight story, what else did they fail to mention? Just to alleviate worry, I would check that out. Good luck.

will e · Oct 30, 2024

Given your symptoms do not be tempted to 'mess' with the new carb. Set the bowl level, check the accel pump is set correctly (lots of videos on how to do this). Set the idle speed and screws. An out of the box holley should run 'pretty good'. Don't get tempted to start swapping jets, accel pump cams and all of the other stuff. That's all for eeking out more power, not getting it running right.

Your goal is to get it to run right first. My first thoughts are ignition and since you've swapped out the carb it's pointing towards that.

What type of ignition is it running now? Is it points? If it is, change them and set them using a dwell meter. This is pretty cheap and easy to do. Even if you are going to swap in something later, the goal is to get it running and drivable.

I'd check and set the timing. Confirm that the mechanical and vacuum advances are working. Don't panic 'how much', the goal is to confirm they are operational. Make a mark on the damper at 0 and about 10 or 12 BTC so they are easy to read. Using a timing light you can set the timing and 'watch' for the marks to move when you rev the engine to confirm mechanical advance and when you connect and disconnect vacuum using manifold vacuum or a small hand pump.

If it still has issues do the compression check. You'll want to know this anyways and if it looks okay then spend the money on a set of plugs, wires, cap and rotor. Those wires look pretty old and might be arching. That will cause a backfire under load.

351mach1 · Oct 30, 2024

Thank you everyone for your responses. It has been very informative and helpful! I am actually on a work trip right now so I wont be able to work on the car for another 2 weeks. Will definitely post an update when I get my hands dirty again.

I went ahead and purchased the Pertronix III igniter and coil with new plugs and wires and everything I need to install the Edelbrock intake. so the plan will be:
-Verify what engine I actually have. Sounds like it might not be the original which would be a pretty big bummer I think. This could also explain the wiring hack job :|
-Check compression of each cylinder
-Install Edelbrock performer #2665 intake manifold with Fel-pro 1228 gasket
-Install Pertronix III ignitor distributor conversion kit along with matching coil and clean up ignition wiring
-Install plugs and wires
-Reset timing
-Check timing chain
-Report back here

Wish me luck!

351mach1 · Oct 30, 2024

I wanted to add what @Sheriff41 responded in my other thread to keep it all in one place:

"I had responded to your post so I'll try to recall what I typed.

Your Problem sounds like you may have a timing issue. Set your base timing to 16° and see if it helps clear up the power and backfiring issues. In the photo, your plug wires look well worn - recommend you replace them.

The 600 cfm Holley is on the small side for a 351C 4v. It will run okay but you're giving away some performance.

The Edelbrock dual plane intake manifold you bought will work fine with your engine and the ram air assembly. You shouldn't have any clearance issues. I run the same intake on my 72 with ram air.

1. I think @giantpune recommended the Pertronix 3 module, which is a popular option. I prefer to retrofit the Ford Duraspark 1 electronic ignition. It is a fairly straightforward procedure and if you use the standard Ford small distributor cap you will not have any interference with your air cleaner. Check out https://pantera.infopop.cc/topic/parts-needed-to-convert-duraspark and https://pantera.infopop.cc/topic/sticky-3-351c-basics-and-performance-tuning

2. @Hemikiller found this video for us:

If you do change the camshaft, check with some of the custom cam grinders, e.g., Brent Lykins https://lykinsmotorsports.com/ so you can get a cam matched to your overall build.

3. Your #3 steps all are sound.

I recommend you get either ARP bolts for your intake manifold from one of the speed shops, or buy all your engine's external fasteners from AMK Products https://www.amkproducts.com/i-kits/ford-individual-fastener-kits/?year_=1971&model=Mustang&category=Engine - 351C

Check all your fluids, belts, hoses (heating/cooling and vacuum), etc.

I'm sure others will add more for you. Keep us posted on your progress!"

Stanglover · Oct 30, 2024

giantpune said:
All the nuts and bolts from the lowes fastener section make me doubt that.
Half the bolts we can see in the engine look like they came from the hardware store.

I was half assed joking!

351mach1 · Oct 30, 2024

Stanglover said:
I was half assed joking!

Ya'll have already shamed me into buying legitimate bolts

Stanglover · Oct 30, 2024

351mach1 said:
Thank you everyone for your responses. It has been very informative and helpful! I am actually on a work trip right now so I wont be able to work on the car for another 2 weeks. Will definitely post an update when I get my hands dirty again.

I went ahead and purchased the Pertronix III igniter and coil with new plugs and wires and everything I need to install the Edelbrock intake. so the plan will be:
-Verify what engine I actually have. Sounds like it might not be the original which would be a pretty big bummer I think. This could also explain the wiring hack job :|
-Check compression of each cylinder
-Install Edelbrock performer #2665 intake manifold with Fel-pro 1228 gasket
-Install Pertronix III ignitor distributor conversion kit along with matching coil and clean up ignition wiring
-Install plugs and wires
-Reset timing
-Check timing chain
-Report back here

Wish me luck!

To circle back on one question out of curiosity, could the 71 M codes be order with a factory ram air or would that mean that mine was aftermarket?

From my own personal experience and unless Pertronix have totally redesigned the PIII for Ford application, I would send it back and buy the PII with matching coil.
A few years ago now, my motor was rebuilt and the builder installed a PIII, probably because he had it on the shelf. It was nothing but trouble from the get-go. The car was put on a dyno so the timing could be checked as the motor went through the rev band under load. The timing was jumping all over the place. To cut the story short, I had the distributor run on a distributor machine where we could actually see the top plate not only move sideways, reducing the air gap to practically nothing, it could also be seen lifting on one side. This proved the reason for the timing jumping around. What could be seen was there was a cheap plastic "bearing" between the two plates which was allowing this movement. I sent it back to Pertronix with a strong letter and they replaced it without question or reason with a PII and coil. It's been no trouble since.
So, unless Pertronix have now installed a proper bearing similar to the Ford Duraspark, then don't waste your money would be my advice. On a positive note, I think the PIII would bee fine electronically, but not mechanically for the Ford application. Its' a shame they chose to cheap out on construction because a PIII would be in my car now.

Stanglover · Oct 30, 2024

351mach1 said:
Ya'll have already shamed me into buying legitimate bolts

Your manifold is a "spread bore", secondaries larger than the primaries.
Without an adaptor, a standard bore carb will not fit and seal.
My advice would be ask before buying. Oops, my bad, I did say I didn't read it all. You are installing a Edlebrock manifold.
..

Bobby · Oct 31, 2024

351mach1 said:
Hello all! This is my first technical question post. I just purchased a 71 Mach 1 and need advice on troubleshooting steps and where to go from here.

Quick backstory: The car is an M code with Ram Air so I am assuming the ram air was aftermarket as the wiki says the factory ram air cars are Q code. The vehicle came with basically no history so lets assume we don't know anything about its past life. The only clue I have is that at some point the factory 4 speed was swapped for a C6. The P/O claimed that it was likely they rebuilt the engine when they did the swap based on how good the engine looks. It's also possible that they just threw a different engine in when they did the swap as I have not confirmed whether the engine block number matches the vin. It is definitely a 351C 4V and has a stock split bore intake manifold. I have an in depth mechanical background specializing in diesel truck repair but have never touched a carburetor; so while I may be ignorant to how to tune a carb, I do know how to turn a wrench.

Problem: Engine runs and revs ok but when in gear, it has no power, backfires, and has a big hesitation when you hit the accelerator. None of the interior gauges work and the wiring harness is pretty hacked up. P/O claimed that a month ago they borrowed a friend's edelbrock carb to put on there (to replace the Chinese copy that was currently on there) and that it ran just fine so it just needed a new carb. I installed a new Holley 600 CFM Street Warrior Carburetor and it runs exactly the same as with the chinese carb so it would appear that there is more to the story.

Goals: I want this to be a reliable weekend driver with a good bit of get up and go. From my brief research it seems that I could easily pull 400 HP/Torque from this engine with minimal upgrades. I don't have an unlimited budget and will be trying to save on costs as much as I can but am also willing to buy high quality parts if they will last the lifetime of the car.

So far: I purchased the Holley carb and have also purchased an Edelbrock performer #2665 intake manifold. I have not installed the intake yet. I plan to install the intake and replace the ignition system and perform a tune up at the same time.

Questions:
1. What ignition system to go with? I am seeing many different recommendations on several different forums. It appears that the Ram Air will limit my choices. I like the idea of the MSD plug and play options but everything I read would make it seem that they will not fit with the ram air. How much of a difference does the ram air make? If my car didn't come stock with the ram air, should I convert it back? What distributor is recommended with the ram air? It also looks like I need to choose a distributor that is compatible with the camshaft; due to the unknown history of the engine, how do I verify the camshaft?

2. Due to the unknow history, is there a way to check the timing chain and gears without pulling the front of the engine apart? Should I just plan on doing the timing chain regardless? If I have to dig in there, should I also just do the camshaft upgrade at the same time or save it for down the road?

3. What steps should I be taking here to get this engine running correctly? My current plan is to:
-Check compression to get an understanding of general engine health
-Install edelbrock intake manifold and Holley carb (any must know advice on the intake install?)
-Install upgraded ignition system (need suggestions on what to go with)
-reset ignition timing, perform tune up (plugs and wires) and see how she runs.
-Verify healthy timing chain

Other desired upgrades: I would like to upgrade the exhaust and camshaft. Suggestions?

I am currently away from the car on a work trip so wont really be able to verify anything until I get back to town. I plan to buy the shop manuals and the 351c rebuild manuals. I did snap these photos before I left. Thank you for any and all help/advice.

View attachment 94750
View attachment 94751

You have a spread bore intake which would require you to get the Autolite 4300D spreadbore carburetor. Those old carbs are available rebuilt and re-engineered so that the inherent problems experienced in the 1970s are no longer a factor. The 4300D would cost you around $900-$1000 when they are available. The new carb you bought is not comaptible with the spreadbore intake. That's why you had backfiring and kerplunk acceleration. Get rid of the current intake and install your Edelbrock. Depending on your budget or fantasy budget, you might consider going with a throttle body EFI. I went with the Holley Sniper mated with the Holley/MSD Dual Sync distributor. The Dual Sync distributor and Holley Sniper is a marriage made in Heaven. No arguments over money, dinner, sex or any other domestic issues. The deal maker for me was the MSD Dual Sync has a low enough profile to allow you to use the low slung Ram Air air cleaner with good mating with the foam gasket to the hood plenum. All the other aftermarket Distriutors are very TALL... No way to fit the Ram Air cleaner properly. The Sniper and Dual Sync are available almost anywhere. Getting the proper fuel pump was limited. The only available pump is from Aeromotive. They combine their fuel pump with a new gas tank. That system will run you about $700. Like you, I'm not much of a carburetor guy but am handy with tools and have done nearly all the upgrade and mod work myself. I've rebuilt engines but have never built a hot rod engine from scratch. I had the good sense to consult with people in the know when compiling all the parts and sent everything to a machine shop. I'm a stick shift guy and loathe auto trannys in hot rods. I've worked on manual trannys in the past and they make sense.....

https://www.ebay.com/itm/2856389639...MH6BeVjnzp7cS/tPhtYdaBQw==|tkp:Bk9SR56m967cZA

https://aeromotiveinc.com/products/gen-ii-stealth-fuel-tank-71-73-mustang

351mach1 · Oct 31, 2024

Stanglover said:
I didn't read all your post (yet), but the first thing I noticed was that the intake manifold is wrong for a 71...... unless someone put an aluminum Boss 351 intake on it!! You may have a 72 motor which would be a Q code. You need to check the block and date numbers located above the starter as well as the partial VIN stamped on the back left side block just under the head. It ought to match the car's VIN. You could also pull the valve covers and look at the date codes between the springs.
71 M code has very large intake ports and won't match the 72 intake
71 M code did have ram air but optional. Mine doesn't unfortunately. However it the motor is indeed a 72, the ram air could have been added.
Sorry but that's my unqualified thoughts so far.

Just speculating here but the hood of the car is painted in the Boss color scheme. Maybe a P/O was going for a Boss tribute? We will see what the numbers say when I get back to the car!

EDIT: This could also explain why the (potentially) 4300D Spreadbore carb is missing as well; as those seem to be highly valuable

Stanglover · Oct 31, 2024

351mach1 said:
Just speculating here but the hood of the car is painted in the Boss color scheme. Maybe a P/O was going for a Boss tribute? We will see what the numbers say when I get back to the car!

Yeah, it gets to be fun (or not so much) digging through the numbers to find out what exactly was done to your car.
Bottom line; body condition, mechanically sound and overall a good buy. If it's not a concours car, then make it the best it can be to suit your taste.
Personally I like to keep the factory look as much as possible. Others like a custom build or a tribute, your choice.

351mach1 · Nov 13, 2024

Alright, so after being away for work for 2 weeks and barely able to think about anything else but working on the Mach 1, I was able to put a few hours of work in.

First I installed the edelbrock intake as that was definitely an issue to have an intake and carburetor that matched. I removed the old cast iron intake and from what I gathered, this is an intake off a 73 cobra jet. I need to purchase a borescope to try and see if I can decipher the head and block numbers. I didn't pull off the valve cover as someone above suggested but I may do that if I can glean any more useful information by doing that. I am leaning toward believing that the engine was rebuilt at some point but still unsure the vintage of block and heads and what work and quality of work was completed.

Next I wanted to freshen up the ignition. I purchased the pertronix 3 but after a few replies above, I haven't broken it out of the box yet. I figured I would try to see if I could get the engine running as-is and leave the pertronix in the box in case I wanted to return it. As it turns out, I believe I have a Dura Spark ignition which some of you recommend. I believe I read somewhere that some California cars came with the Dura Spark and this car is from California. I changed out the cap, but the rotor I bought doesn't work. I installed new wires (which are ridiculously long) but didn't change the plugs as I wanted to confirm what ignition I had to then determine the correct gap for the plugs.

I started her up and she idled fairly smooth. I let it warm up for awhile and then tried to rev the engine and got some pretty bad backfiring. The backfiring was a bummer so I decided to start looking into resetting the timing. Before I reset the timing I checked the timing chain slack and unfortunately it seems that I have somewhere in the neighborhood of 8-10 degrees of slack. So that's a problem I do believe. Next I found TDC and the distributor appears to be in the correct position. I did not remove the distributor and re install as I didnt have enough time. I may try that but I think the timing chain slack could point to needing to replace the timing chain before messing with the ignition further. Also, the ignition and engine wiring is a mess and I could really use some advice on how to clean this up and confirm that the ignition is wired correctly.

Questions for you all:
1: Would my next troubleshooting step be to replace the timing chain before messing with the ignition further?
2: Is this a dura spark and what the hell is going on with this hack wiring job.
3: What gap should the plugs be for this ignition?
4: Should I keep the Dura spark or swap out for the pertronix 3?
3: Any and all advice appreciated!

giantpune · Nov 14, 2024

1) If you've done the check of moving the crankshaft while watching the distributor rotor, and determined you have 10 degrees of slop, that pretty much seals the deal. You can repeat that test to be sure. But it doesn't lie. If you get the same result, a second and a third time, the timing set is toast. You could cross your fingers and hope its play in the distributor gear itself. Test that by seeing how much you can rotate the distributor rotor/shaft while the rest of the engine sits stationary.

2) That looks like it may be the connector for the engine wiring harness. There may be 2 similar connectors there in the same spot. If so, you'd look at the wires coming into them to tell them apart. The one just about everybody has is the one with wires for the temp and oil pressure, and a feed for the ignition.

https://www.npdlink.com/product/wire-assy-engine-gauge-feed/146041/202876?year=1971

Stanglover · Nov 14, 2024

Here are examples of head numbers and the block numbers (from my 71)
You missed an opportunity to read the head #s when the intake was off unfortunately. In this example, the head shown is D1AE on 1 runner and GA on another. The date code is 0M1 or 1970- December -01. The block date code is 1971 January 07. The car was built on February 22 1971.

As you have a DuraSpark dist. in there, my choice would be to rebuild that if necessary and get the best out of that rather than swapping it all to Pertronix as I believe you'll need a complete distributor. Again, I would not use a PIII Ford application based on a previous bad experience.

EDIT: I thought I had seem a description of where to read the original partial VIN on this post, but checking back I didn't see it.
A partial VIN will be at the back of the left side block just under the head. It might be hard to read due to poor stamping. You would likely see something like this 3f 123456. The 3f would confirm it is a 73 block or complete motor if the other numbers match. If the first number is NOT a 1, this motor was not out of a Mustang. If I remember, 5XXXXX would be a Cougar.

351mach1 · Nov 14, 2024

DOH! I knew the casting numbers were under the head but I thought they were under the exhaust ports not the intake. Missed opportunity. I did go ahead and pull the valve cover and get the date code which indicates May 73. I was also able to get the vin on the back of the block. I will pull the starter off to get the block casting number when I get a chance. Please help me decode this block vin. (73, Atlanta plant? Which would mean this isn't from a mustang)

I checked the timing slack 2 more times and its still indicating about 10 degrees of slack. I tried turning the rotor as suggested and it does not turn at all clockwise but turns about 5-10 degrees counterclockwise but it seems to be designed that way. See video.

Current thoughts: If this is the detuned 73 Cleveland not from a mustang, is it worth it and do I want to put the effort into getting this back on the road as is (the auto transmission is a total mess as well) or do I try to find a correct M code 351 and manual transmission to bring the vehicle back to its original state?

351C where to start?

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