Which Oil weight
 

I just finished installing the rear oil seal retainer, thanks to everyone who helped with advice. Now I want to put some oil in this beast and see if it runs. My manual says to use 20 wt oil is that correct. I have never heard of an engine that uses that kind of oil. What do people run in a 312 Y-block?

I just spoke with John Mummert who said that he suggests using Chevron Delo Diesel oil 10-40W because it has the additives that the older style engines need. Does anyone have experience using this kind of product in a Y-block?

Run 5W30 regular oil (not synthetic) in my Y-Block.
Fred