Looking to boost the power of my 318

Hey guys, I have a nice fresh .030 over 318 in my station wagon and I think it might be suffering from low compression. It has a set of fresh 915 j heads on it and the pistons in it are the trw forged units. Looking at the specs of the pistons themselves, they are supposed to come out to 8.2 compression with 68cc heads and I know for a fact my heads have bigger chambers than that. So I was considering swapping the slugs to a set of kb 399s, which are supposed to have 10.4 compression with 68cc heads.

Anyone have any input?