Flat Top Pistons

I'm getting parts together for my LA360 build and noticed that hardly any companies carry dome pistons. The flat tops in the motor now are fairly new but I don't know where they came from. They are true flat tops with no valve reliefs.
Are there different flat tops that raise the compression ratio? I'm running stock stroke, no deck work that I can tell, and the heads are stock smog 70's heads (041 I think).