452 heads on a 1965 Wedge ?

The heads I have are the original 516 ones that are closed chamber, with flat top no notches.
The factory compression is 10.3 to 1, which I feel will be too high for pump gas

My question is :
To calculate the cr with 452's, do I find the cc's of the heads and subtract the difference,
What I don't know is how many cc's are in a point of compression ??