Slant six carb help

I have a slant six with a holley 600 model 80457-2 with vac secondarys and 64 primary jets.I was going to change carbs since it is to much carb for the engine . I have decided to unhook the vac secondarys and jet the carb down as one member suggested instead of changing everything. My question is what size jets should I try.Did any of these engines have 2 barrel holleys and what where there jet sizes