I had flattop pistons at first for my 440/493 as I was going to use 84cc RPM heads but when I decided to go with the 75cc EZ heads I switched to the D-dish type of piston. It still has a flat portion to get good quench but dropped my comp from about 11.8 to 10.6 which is what I was shooting for in my pump gas build. I was lucky as I traded my flattop pistons to my brother for some Hughes roller tip rockers and then bought new pistons. Good luck with your build. Ron