Well my math says that if you had 100 VE your 502 spining 5000 rpms would you 726 cfm. So a 700 or 750 would work for you. If you go to a vacc 2nd carb you will save some fuel. (no squirters) You will see a big reduction in the use of fuel if you always on and off the throttle. If you keep your speed constent, you will really see no diff.