Get out your measuring devices and tell us how far down in the hole those pistons are at TDC. A flat top piston engine can make power. A set of closed chambered hears or a set of aluminum's can make it sing.
The pistons don't look like they are very far down from the deck surface, I'd say closed chamber heads with around a 62-64cc chamber and 0.039 thick head gaskets should put you around 9.0:1 - 9.25:1.
