I have another Question: I want to get my motor 340 back to 10to1 comp. is the 70 340 pistons different from my 73 ones and will they give me my desired net of 10to1?
They should, but you have to check you deck hight, also depends on the combustion chamber volume and gasket thickness. I'd run large port heads on a 340.
920 heads are the best small port, small valve heads.