I feel for ya' as i'm in the same boat right now. Those pistons in the pics look like a stock replacement type piston, probably a 1.74 CH. Depending on how much the heads have been milled your comp ratio will be in the 8 to 8.5 range. That's why i choose a reasonable intake duration at .050. Should still be a pretty strong runner with the other bolt on's your using.
I looked up Speed-Pro pistons and they are 1.76 CH. but i'll still stay with the same comp. ratio guess.