As I have come to understand it, one of the great things about the Quadrajet design, is that there's no such thing as too much carb;
the "800cfm" castings were used on a variety of engine combinations - many of which, when conventional logic is used, would indicat that 800cfm is too much.
IIRC the spread bore design essentially feeds as much as you need.
I would use the best core carb you have as the basis of your carb.
But that's as far as my opinion goes...