71 and 67 318 heads??

Probably next to zero difference other than the casting number. 1.78/1.50 valves, open chambers etc. Both lack hardened exh valve seats. Why not get a set of the 302 heads and plop them on - wont cost that much if you have to redo a set and they will have closed chambers (higher comp ratio) and hard exh seats. With a little intake port work you'll have better heads. my 02.