My turn to beat the dead horse! I skimmed the preceding posts, and found some really good thoughts put forth. For what it is worth here is what I do when it comes to engine oil for our vintage pony cars.
Short Version. I use AmsOil Z-Rod 10/30 synthetic oil in our vintage Mustang/Shelby engines. I also use Motorcraft FL-1A oil filters as they are made with excellent quality.
For old school flat tappet engine you are going to need an engine oil that has Zinc in it, or add Zinc with an off the shelf additive. If you do not do that you risk having your camshaft lobes and lifter faces wear very quickly and very badly - in some cases in a very short period of time. The damage is not reversible, and will require replacing a lot of parts. It is totally avoidable by using the right kind of oil - both with Zinc, and the proper viscosity.
Before getting into what we use, I just want to share a bit about why Zinc is no longer added to modern engine oil. Zinc in the oil can and will end up getting into the combustion chamber, especially with an engine with some wear on it. From there it goes out the exhaust, and in exiting the exhaust ports it ends up contaminating the catalytic converter platinum and palladium surfaces. That causes the catalytic converters to lose their ability to act on unburned Hydrocarbons, Carbon Monoxide, and Nitrous Oxides emissions, and converting those harmful emissions into harmless water and (less harmful) Carbon Dioxide. The Zinc coating on the catalytic converter internal media surface causes elevated levels of air pollution beyond the levels they could be reduced to were it not for the Zinc coating the catalyzing materials inside the converters.
That begs the question of how the lack of Zinc impacts modern engines. Manufacturers have moved to valve train designs other than the traditional flat tappet design. We are seeing hydraulic roller lifters and overhead camshaft designs in modern engines, which do not need Zinc to be well protected by a high quality engine oil that is available in an adequate amount, temperature, and cleanliness.
For our First Generation Mustangs and Shelby we use AmsOil Z-Rod 10/30 synthetic engine oil. Their Z-Rod line of oils have Zinc, and are designed to properly protect those old school engines. Any time I see AmsOil pitted against other oils their products always come out on top. That is not to say the other brands of oil are not good. There are a lot of excellent, and more than adequate engine oils (with Zinc also) on the market. Using AmsOil is really over the top compared to what I could get way with, but such is how I do things. I am a bit uncovered by Billy Joel in his one song where he says, "I don't now why I go to extremes
." I have some guesses why I do the things the way I do them. In the case of selecting AmsOil it is that I am trying to preserve the integrity and condition of our old engines for as long as I can, using the best product I have found.
Okay, so that is the product line I use. Now it comes down to viscosity. The recommended viscosity from Ford is 10/30. So that is what I use. When (if) the day comes that I begin to burn oil I will move to their 10/40 viscosity (aka "weight") Z-Rod oil. They have 20/50 viscosity for Z-Rod as well, but I think once 10/40 is no longer able to help control oil being burned due to normal engine wear I will opt to undertake rebuilding the engine, using really high end parts to ensure an extra long life (and some Go Go upgrades just because). Not to get too far off track, but some of the internal upgrades will include hardened valve seats, bronze wall valve guides, and Perfect Circle real Valve Stem Seals as opposed to using the oem style upside down umbrella oil splash redirection excuses for oil seals. That, plus a high capacity oil pump, high quality forged aluminum alloy pistons (balanced engine), high quality oil and compression piston rings, and Clevite 77 main and rod journal bearings, plus a roller camshaft and lifters, and a double roller timing chain and gear set made of only metal (no plastic/nylon tips on the camshaft timing gear teeth will help make for a very long lasting engine. When combined with the use of AmsOil Z-Rod, snd s high quality oil filter, that will give the engines the potential to outlive me, and perhaps the next generation of caretakers after me.
So then, now it is time to beat a slightly different dead horse a little. I am pretty picky about the oil filters I use. Motorcraft FL1A oil filters are very well made, and are made by Purolator. There is also have a heavier duty line of Motorcraft racing oil filters, but I never felt the need to move to them. It may have a lot to do with reports of them leaking when the FL-1A filters did not leak (base square cut seal issue, see attached user responses). I also like the NAPA Gold or Platinum oil filters, as well as Wix Extended Performance oil filters (NAPA Gold & Platinum oil filters are reportedly made by Wix). I have never used a Purolator branded oil filter, but given the quality of the Motorcraft FL-1A oil filters that they are reported to manufacture, I am betting Purolater brand oil filters are also excellent. I have seen several comparisons with Purolater filters and they hold their own in the company of other high quality oil filters. I also like the Royal Purple oil filters and K&N oil filters. AmsOil offers their brand of oil filter, but I don't know who makes them, and have never really looked them to see how they fare when compared to these other really high quality oil filters.
Please take note I have excluded (regular) Fram oil filters from my range of oil filter selection suggestions. 'Nuff said. heh heh...