i have set of 71' 402 big block heads with the casting 292. does anyone know the combustion chamber size off hand? these are not closed chamber heads, they're open chamber with a cut back by the exhaust seat. i need to get my compression up to 9.5:1-10.0:1. i have 17cc dome pistons, my bore is 4.155,stroke 3.76, deck height is about .010, and running .020 head gasket. i can have the heads milled to get my compression up, but i need a starting point, help would be appreciated!