Carb too big?

As killer6 stated there are different standards when measuring cfm ratings of carbs. A 500 CFM Holley 4412 two bbl flows almost exactly the same as a 390 CFM 4bbl.
Believe it or not, the 390 four bbl would be better on a street car. Even though both carbs have the same total CFM, the smaller primary barrels on the 390, will give better throttle response. Theoretcly the 4 bbl should get better fuel mileage, also. At part throttle, the higher air flow velocity in the smaller primarys, willl result in better fuel atomasation(sp). Plus the 390 has a smaller accelorater pump (30 cc as compared to 50 cc) so small movements of the throttle will not shoot as much fuel.