Well, .012" inch below deck is right for these KB107 pistons and the stock deck height and stock rods, and that seems like 'slightly' IMHO.
So perhaps the heads have been milled a bunch. Do you recall if the 'open' part of the chamber on the heads was very shallow? The stock area is around .090" deep; if the heads were milled about .060", then the chamber size would be down in the low 60 cc range.
And using nail head valves (straight across on the main surface in the chamber) would lose another few cc's. And then there is the head gaskets.....lotsa variables.
I think I would still try one more compression gauge....
