I've done quite a bit of carb tuning with a wideband. I put together a data logger that includes left and right wideband AFR, manifold vacuum, RPM, speed, and knock. I have the parts to add TPS and fuel pressure, but .....too many irons in the fire.
Set idle mixture using highest vacuum reading or RPM. If it's an automatic, set that in drive. The AFR you end up with is what your engine likes. Don't try to hit a target, unless you have to for some sort of emissions test.
I record both low speed and high speed cruise AFR values. To do that, you need to know the RPM you're observing AFR at, and the transition RPM where your carb begins to pull from the boosters. LS cruise runs off the idle, aka low speed, circuit. It will have its own AFR that is controlled by the low speed air bleed, idle feed restrictor, and mixture screw adjustment. High speed is, as the name implies, when the engine is primarily pulling through the boosters. High speed air bleed and main jets are the main control knobs here.
The 50mph readings you have are probably transitional....better to be clearly on the LS and clearly on the HS circuits to get definitive data. What is the RPM? High Speed with a 750cfm should put you on HS circuit at about 2500 RPM. I usually record LS cruise at 2000 RPM and HS cruise above 2500 RPM.
For a street car, I am tuning for 15:1 AFR on LS and HS cruise. That requires a fairly lean main jet and the ability to change out your IFR's and possibly, air bleeds. This tuning will uncover any sort of stumble you may have. It is not necessary to tune this lean. You'd be fine at 13:1 and your plugs will look ok or maybe slightly rich.
For wide open throttle (WOT), the main jets, PVCR's (power valve channel restrictors) and the PV, itself determine the AFR under those conditions. Engines from our era tend to like 12.5-13:1 AFR. It's better to be too rich than lean. I find that a moderate street cam, giving 12" vac idling at 750 will like an 8.5 power valve. That enriches the mains sooner. than a 6.5 or any lower, for that matter.
Start with tuning for the LS and HS cruise numbers you're after. The HS cruise will establish your main jet. With that, you can tune for WOT and alter the PVCR jet to get to the 12.5-13 number.
In summary, your idle is probably lean...mine likes 12-13...about like WOT.
Your 50MPH is very rich and depending on RPM is either a main jet (HS cruise, or a IFR, LS cruise) that needs to change.
Your WOT numbers look pretty good...they are safe but you won't know how to improve w/o some sort of performance device or drag strip. I use a device call Dragy for my comparisons. It's a lot of fun to see how your changes impact the performance....highly recommended but wish it had a way to download.
If you made it this far, congratulations! If I can be of further help, feel free to ask.
Edit: Shoot, I just saw that you're running an Edelbrock carb....all my inputs are for a Holley. The circuits will control the AFR in a similar manner, but I'm not familiar with Edelbrock carbs so I can't tell you how the holley circuits cross over to the Edelbrock.
By the way my rear end ratio is 2:75.
