302 heads are ok, but there are some out there with cracks... Make sure if you get them that they have been checked...
The early 273/318 heads do not have a known cracking issue...
I put a set of 67 273/318 "920' heads on a 72 318 to help increase the compression about a half point... I had my head guy port them, install hardened seats, then install 360 valves in them 1.88" intakes and 1.60" exhaust... He claims they will flow as well as a stock 360 head or better....