Rpm 340 Cyl heads on a 318 !

Dear bad
by notching you are looking at a half moon out to the combustion chamber - not the gasket pretend your are flying through the intake and what do you see when you come through the valve- iron walls are not good for flow
are these Iron heads? post up the casting number- I have no idea what an RPM is?
here is a good place to start for a piston search click on the picture of the piston to pop up compression ratios with different head cc's
Chrysler : United Engine & Machine Co. Incorporated, Performance Pistons
but you have to know your head cc's and not just the advertised/ published data- measured cc's
once we know your casting number or head mfg members can give you a ballpark for what they really are till you get them cc'd (that's a DIY task)