CR calculation, deck height/effective dome volume?

Yep, she's ben decked. I'm thinking .020" from my piston measurement (and I measured all 4 corners to make sure the block was square), but since this motor came my way with most of the machine work already done, that's just my guess. With a static CR I've figured at 10.4-1 (my X-heads measure 63.6 cc) I'm wondering about ways to lower it now.