273 Cyl Head Differences

66fs said
920 heads are 67 heads that use the standard 3/8 intake bolts that have a 9/16" hex head. 315 heads are typically 64-65 heads that use 5/16 intake bolts on a different angle that have a 1/2" hex head. However I have a set of 315 castings that use the standard 3/8 intake bolts that have a 9/16 hex head. Not sure what was going on but appear to be virgin OEM heads. They even have the steel shim head gasket witness lines from the original .020 thick 273 head gaskets. Best advice I can give is to ask what size bolts those heads are tapped for. There are 66 heads that will interchange with the 920s and you can also use any 318 heads with a slight loss of compression.

Interesting that you mentioned those 315's with the 5/16 intake bolts. I thought I was the only one who ran across those and had many arguments about them until I physically showed them to a few people. Not only that, but, I also had a pair of 920's with the 1/4 intake bolts! There must have been both rough castings produced, or, at least both co-existed on the shelf at a certain time before the final machine work was done.