How do I calculate compression or guess

Well, you could "ball-park it", to help with piston selection. Then when the pistons are finally in the block, you can work out the rest.
Or you could mock it up with what you got,get an in-the-hole measurement for that piston, then pull it out and measure the compression distance. A little math can then get you close to the actual block deck height.Close to, but not exact.
But I just gotta ask; What are you up to?
And why/how did you come to choosing those cams?Are you trying to work backwards to a particular Dcr number?.