As for the viscosity, we either ran straight 30 year round, then 10W-30, and later possibly 10W-40. This is in N TX, so it's not usually as cold as in the norther regions.
When I got my '70 DH43N, I started out with what the dealer put in it when they changed the oil for their used car checkout. Then, after chasing a "4500rpm surge" that would not go away and wanting something better, I settled on Castrol GTX 20W-50, which many people called "motorcycle oil" in 1975 (as that was usually what it went it). I figured that if it could stand up to autobahn speeds in a smaller, Euro-sized engine at higher rpms, it should do just fine in a larger American V-8 with more generous bearing sizes and lower rpms. AND, that surge went away after that change, too.
To me, I feel that the oil companies can blend a really good oil (base stocks and additives), but you might have to look a bit to find it), which is why I regularly monitor
www.bobistheoilguy.com forums, where some PQIA results are also posted. BTAIM
I recently found some Castrol black-bottle Edge that is NOT Dexos approved (key thing these days) AND has the "SL" rating, which means right at 1000ppm of zddp in it. I also went to Rotella T6 5W-40 in my '77 Camaro. Key things: readily available everywhere, decent pricing, and a good syn oil still with over 1200ppm of zddp in its latest blends.
When I got the Camaro, after the 3000 break-in period, I put 20W-50 GTX in it and the oil comsumption went down to 1/2 qt per 4000 oil changes. When I did the cam, timing chain, and intake upgrade at 92K miles, I (as others) was startled at how clean the lifter valley was. The only accumulation of "gray stuff" was in the small recesses where it could settle out and was liquid enough to remove with a fingertip. Plus, very few deposits on the bottom of the heat crossover shield on the bottom of the intake, which also amazed those used to seeing what other brands normally put there. In other words, it was danged clean inside, which made me smile!
As noted, adding lots of zddp to a detergent oil can compromize the detergency additives. Seems like there is one Joe Gibbs Racing oil that has 3000ppm of zddp in it? But that oil is meant more for a 500 mile race than a 4000mile street-use oil change, I suspect. So you can get too much of a good thing!
One other issue is that there are other anti-wear components in motor oil than just zddp and the base stock oils. So zddp is not the only guide in that respect . . . at least that's what some claim. 1000ppm of zddp in a syn oil is fine, but a dino oil needs more like 1200-1400ppm (as some of the normal Rotella diesel oils have in the . . . NOT the recent "gas truck" oils which are Dexos-compliant).
The oil of your choice, viscosity of your choice, with a quality OEM-level oil filter (Motorcraft in my case as they are available at a good price, FL-1A for the long filter), changed about every 4000 miles (the old Chrysler oil change spec, when the cars were new, with the 5/50 warranty) should work fine without breaking the bank.
Just some thoughts,
CBODY67