in my own cars i use and have for years Shell Rotella T 15w40 (diesel engine oil)
it is entirely compatible with the relatively ancient red block.
it is a superb product:


""""We still sell Rotella T 15w-40 CI-4 in 55 gallon drums, but not in smaller packages. It has approximately 1400 ppm zinc. You can buy this from a shell lubricants distributor.
Since Oct. 15,2006 all small packaging has been Rotella T with triple protection 15w-40 CJ-4 and it has approximately 1200 ppm zinc. This is 50% more zinc than current passenger car motor oils which contain approximately 800 ppm zinc. Passenger car motor oils had approximately 1200 ppm zinc prior to 2001. In 2001 the zinc was reduced to 1000 ppm and in 2005 reduced again to the current 800 ppm.
Thus, the new Rotella T with triple protection 15w-40 CJ-4 has the same zinc content that passenger car motor oils had in 2000 before the current problems with flat tappets began.
However, zinc compounds are not the only additives that can reduce wear. We were able to reduce wear approximately 50% with the new Rotella T with triple protection 15w-40 CJ-4 formulation.

This is from a staff engineer in Houston, Texas. """"""


this oil meets all passenger car specs for cars of our vintage

FYI... tractor supply carries this product in gallon containers and 5 gallon containers