I'm not sure what the aftermarket 950 bodys flow, the Holley 950HP will flow around 880 CFM on a flow bench. The Holley 850 double pumper with the choke plate removed will flow close to 920 CFM, depending on the carb. 500 C.I. will respond to a bigger carb better than a stock stroke BB will but alomost any carb will work. The size depends on how mauch HP you want to make and the driveability you want to end up with Think twice befroe buying