How far in the hole?

They also used metal shim gaskets that were super thin from the factory.

I've measured 9.65:1 with known 62cc heads and pistons that sit .011" in the hole, on ring lands that sit higher than stock, with .028" gaskets. Those 1121Gs are 4.140" diameter.

I think you could fetch close to 9:1 with the right gaskets and heads on a stock, early 318 bottom end.

Advance the cam to fetch more overall cyl pressure.

PSI is what everything accumulates to. PSI = power.