Polishing the chambers make them bigger than stock
Cutting the heads makes the combustion chambers smaller
As far as your reading on that digital micrometer are you putting any pressure on the gauge to make it tight up against the head? If so ,don't
Do you have a decent regular, non digital, outside micrometer that you can set the calibration on? If so compare your readings between the two gauges and let us know what you find
If not don't worry about that now, you already know the CC
I have seen as much as 4.2 CC differences in stock wedge and hemi heads between all four chambers on those heads