compression?

It's easy to actually measure the cc's of your heads. Get a piece of plexi glass that is big enough to cover the chamber. Rill a small hole (~1/8") in it so it will be near the edge of the chamber. Go to the local pharmacy and get a plastic syringe that is graduated in cc's (one that has a ~100cc capacity will be the best).

With the valves installed and a spark plug installed put some greas on the edge of the plexi glass to act as a seal. Using the syringe fill up the chamber keeping track of the amount you put in. You know know the cc's of you heads. Check both ends of the head and take an average.

Also, with you KB107 pistons how far down in the cylinder are they? That will impact your compression too. All the numbers you see advertised for KB pistons assumes you have had the deck on the block machined so the piston is even with the deck (i.e., "zero decked").