I have two sets of standard bore 413 pistons but they are still on the rods. I'll have to check if they are flat tops or not. I have a set of new, unused flat top 440, and nice flat top set for 340 (just in case you consider upgrading). I'll check today if my 413s are flat. I am assuming you want standard bore? I also have a set of recently done 906 heads. They would boost your compression up a bit. How about a six pack?