If this is a old engine with lots of miles on it, you have no need for the high zinc levels in race oil or diesel oil. You cam is well broke in and the valve springs are pretty weak compared to high quality race springs. So any oil oil you wish to run will work fine. 10w30 is the same as straight 30 once warmed up but will flow better when cold so you have more lube and less drag at first fire. I run 5w30 in my 250 and dad runs 5w20 in his race motor (469 ci Pontiac), we like the less wear and tear on oil pump drives and gears. Thick oils like 20w50 just cause stain on the pump drive and rob horse power.
Joe
