X or J heads

[QUOTE="Locomotion, post: 1973695401,I think you can get away with higher compression at higher altitudes, but I don't know how to figure that. You can stay safe and cut down the domes, probably to flattops, while saving some weight off of those heavy pistons. (If the block cleans up at .030".)[/QUOTE]

The new pistons weigh 524 grams, I don't know how much an original 340 piston weighs.