I have used the Edelbrock 500 on two flatheads with very good results. I've had people tell me it's too much carb for the motor, but it worked fine. I got good mileage and the motor was very responsive off idle. I had nothing but problems with a 390 and would not use one again. I haven't used a WCFB, but when the four barrel manifold first came out the were designed for that carb. Guys I know that used them were very satisfied.
Another excellent vintage carb that's harder to find is the Stromberg Aeroquad - only used for a few years on Buicks (I think). I don't know flow, but it's comparable to the Carter.
If you can, get the WCFB for a smaller engine like a 265/283 Chevy - it will be better jetted and sized (the main body is slightly different from model to model) for a flathead than a big Buick or Cadillac.
Holley 390 has worked well for me.
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