Caviat - I no longer build carburetors, so the following is information, NOT an ad:
If you were to acquire a professionally restored ORIGINAL Chevrolet 283 Rochester 4-G, AND a professionally restored ORIGINAL Chevrolet 283 WCFB; and take them both to a mechanic you trust.
Instruct the mechanic to install his choice on your engine AND LOCK THE HOOD without telling you which one he installed.
Drive 1000 miles, and keep records of fuel used, driving impressions, etc.
Return to the mechanic and have the other carb installed and lock the hood.
Repeat the 1000 miles over similar conditions, taking notes.
At the end of the second thousand miles, compare the notes. You will not be able to tell if the mechanic actually changed the carbs, or not.
Yes, the Q-Jet is slightly more advanced in design than the 4-G; but the real argument for the Q-Jet is the spread-bore design for LARGER engines. The spread-bore design has no significant benefit for a basically stock engine as small as a 283. How much is slightly? Well, maybe give the Q-Jet 95 out of 100 and the 4-G 89 out of 100. BOTH would be a letter grade of "A" (pretty good
), but the Q-Jet would rate a A+.
Yes, the AFB (the real ones, not the modern imitation) is slightly more advanced than the WCFB. How much? Give the WCFB a 90 and the AFB a 94 (the Q-jet gets the 95 because of the spread-bore design (for larger engines).
Both the Q-Jet and the AFB can be tuned more easily than either the 4-G or the WCFB, but for a basically stock engine - who cares? If you are building a race car, then other priorities (what kind of racing, etc.) would need to be considered.
As far as NEEDED CFM is concerned: Carter published CFM ratings on only one WCFB, the 2493s, specifically designed for RACE ONLY on a Chevrolet 283 in 1957. This carburetor was rated 380 CFM.WCFB flow ratings
My guess would be if Mr. Duntov thought he needed more than 380 CFM, he certainly could have had it!