I know it sounds weak, but it has been proven in short track racing that 2bbl's have better throttle response and make more bottom end power than a 4bbl. I believe it has to do with the fact that a 2bbl carb gives a much denscer fuel/air mixture ratio than a 4bbl.
Even though the secondary plates are closed on a 4bbl you are still pulling air through the venturi.............I agree with you the 2bbl will not make the horsepower of a 4bbl, but the 4bbl cannot be compared to a 2bbl if the secondaries are closed. There is still a vacuum loss even with the plates closed.
I think for your application, I would definitely run a 2bbl on that 413, those old 413's are great motors.

Mark D.

1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline

E. Brookfield, Massachusetts