340 compression test

NO spacers, but you can go thicker on the head gaskets for a few more $$. But, I'd take it apart and research the cam. Assuming the rings and valve job seal the cylinder well two things comprise cylinder pressure: static compression ratio, and the intake valve closing point. If the cam is small, and the static is higher (11.5-12:1 which is easy with the domed old school pistons) you will have high cylinder pressures. I'd say that was woefully undercammed too. But, see what you have first, before you worry about what to buy to fix it.