Four barrel carburetor for slant 6 Offenhauser manifold?

Actually a 383 from back in the day was no bigger than 600 CFM. Depending on year and carb number.
Early 60's 383 AFB's were in the 465-475 cfm range. Chrysler literature called them 500.
It was around 1967 that the AFB grew larger and when the 440 AVS came out it was rated at 750.
If you do a search here on CFM ratings there is a list I believe.
My favorite is the Eldelbrock 500 for street use. I even ran one on a 451 B stroker on the street.