340 with 302 cast head for pickup

...It's hard to call this one without better piston info.....you need to help us to help you.

Are these some forged units or what? Domed or flat-top? Are they truly stock factory pistons? Speed Pro? Sealed Power? Original 10.5's weren't really 10.5 CR in the engine.....

^^Thank you...I guess when it was mentioned a couple times above, the point wasn't made clear.

http://torinocobra.com/Randys_tools.htm

use that calculator...you have to know the particulars, but it's a very useful tool