Carburetor cfm for a mild 318 build

Bewy said

The OP has not given the cam specs, only that it is mild. That means the volumetric efficiency of the engine will be low-ish.....
The VE is highest at the peak TQ rpm, which will be well below the theoretical max 5500 rpm of the intake. VE at 5500 might only be 80%, compared to 85% at peak tq. That equates to about 520 cfm for 318 cubes @ 5500. Better to err on the small side.

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80% ve would be a 400 cfm, think of it this way, that formula if we use it to pick cylinder heads, would mean the total flow for all intake ports would be 400 cfm or 50 cfm per intake port, but that don't compute. What a heads rated cfm has nothing to do with what an engine will displace at rpm, same with carb. Within reason whatever cfm your engine displaces any carb will flow it just at different vacuum level "HG"

What it comes down to is what carb will give you the best balance of power tuneablity and driveablity. And we pretty much know cause every combination under the sun has been tried.