In the picture of post number 7, the deck surface appears to show markings from previous decking. Do you know for sure if yours was previously decked?
As for the numbers, I think I agree with KB on this one, or at least they are pretty close. If we treat that as a flat top piston, which typically has around 5 or 6 cc valve pockets, you would add the volume of that little step around the piston to the valve notch volume, and that is how they get 7.3 cc. But, the numbers say that "flat top" would sit about .018" above the deck, assuming 9.6" deck height, and the numbers measured from 72bluNblu confirm this on his engine. With those numbers in the calculator on the diamondracing.net website, it comes out to 9.99 to 1, and that is including .305" top ring land height.