You need to know what heads you are going to use. This way you can buy a rotating assembly with the correct pistons to match chamber size. This rotating assembly with 64cc chambered heads would have 9.7 compression ratio.
Eagle Specialty Products B13004E030 - Eagle Street and Strip Rotating Assemblies - Overview - SummitRacing.com This rotating assembly with 64cc chambered heads would have 10.3 compression ratio. This would be too high for pump gas unless you have aluminum heads.
Eagle Specialty Products B13404E030 - Eagle Street and Strip Rotating Assemblies - Overview - SummitRacing.com You would use 76cc chambered heads with the above kit for a compression ratio of 9.1. You could also use a 7cc flattop pistons for a compression ratio of 9.7 with 76cc chambered heads and this rotating assembly.
Eagle Specialty Products B13005E030 - Eagle Street and Strip Rotating Assemblies - Overview - SummitRacing.com Please read some of the reviews on Pro Comp products from a google search.