I picked up a 394 the bell housing number reads 585786-4 1/8 the head number is j 684633 . I think the block is 1964 ultra high compression and the heads are from a 1963 330 hp . That's what I have read. And the question is the pistons high compression they look like high compression pistons but there are eye brows on both sides. and the cylinder bore is 4 inch .167 thousands plus or minus .002 . This is the way I got the engine the walls look great with very minimal scratches hone marks are there . Also on the piston is .040 . Head gasket .025 thousands