I have a 400 that has no heads but I have a pair of 1985 TPI 305 heads laying around. Would I be able to use them on the 400 if I had the holes drilled for the steam ports? Also how much would that raise the compression.
Thank you

 

Yes you can use them on a 400SB after drilling for the steam holes.

The nominal chamber size on those heads is 58cc's
To calculate your compression ratio with thoses heads you need to tell us a bit more about the 400.

Piston dome/ dish volume valve relief volume, piston deck clearance at TDC.

 

Those heads will over hang the cylinders horribly. The 305 has a bore of, what? 3.766" and the 400 has a bore of 4.125" leaving 0.359" of head surface over hanging the cylinder bores. And getting gaskets to seal properly may be a problem.

 

Just did a quick calc and compression would be at 11.7:1 w/ a set of FT's. A -18cc dished piston would be required to get a pump gas friendly 10:1. Both those are with a .041" think headgasket and 9.025" deck height.