Well, your options are either to get bigger valves put in the 302 heads and retain them for the compression advantage, or, change to the 915 heads and make up the compression difference in a piston change or milling the snot out of the 915s. Either way, if your engine is making much over 300 HP, you will benefit from 2.02s and 1.60s in either head, so you're gonna spend a chunk in the heads anyway. If you retain the 302s, you will only need to spend the chunk in the heads for larger valves and not in the short block to raise compression. But all that is just my humble opinion.