Holley also assumes that all calculations would be based on a V8 engine with all cylinders drawing from all carb throat simultaneously. This means a single plane manifold, not a dual plane, divided single plane, or "360°".

If using a V8 with individual throttle bodies such as stack injection, the formula will invariably return a size far too small to work. E.g., if a single Holley 4500 supplies 1,000 CFM to a 500" engine at 7,000 RPM, the intuitive assumption is to divide the 1,000 by 8 to get the ITB CFM, or 125 CFM each. This is only slightly more than 1" diameter...
There is a correction for 6 cylinders or less supplied by the same carburetor, multiply this number by the usual Holley formula:
7 or more cylinders: 1.0
6 cylinders: 1.1
5 cylinders: 1.3
4 cylinders: 1.6
3 cylinders: 2.2
2 cylinders: 3.3
1 cylinder: 6.6

The CFM for the 500" engine would each be 825 CFM (assuming no manifold volume). At about 125 CFM per square inch, this makes the throat 6.6 square inches, or about 2.9" diameter. How odd, that's the size of the Crower BBC stacks...