I'm not going to go into a big story here but that combustion chamber can cause problems if you shave too much off.
Now i have said that. Get some clay and roll it into some string and then trace your combustion chamber. Then lay it on something flat and measure how big of a circle you have. now .7854 x bore x bore x stroke so let's say you clay string circle is 3 inch so .7854 X 3 x 3 x let's say a .020" head cut. .7854 3 x 3 x .020= .141372(CI)X 16.387=2.3166 or 2.32 CC.
Huh? Wait a minute. With these combustion chambers there can't be a set milling amount, because the first passes will lose more cc per thou. Due to the shape, the more you mill, lesser and lesser cc'S come off per thou. Is this what ya mean?