With that having been said, I think you may be much closer to solving your problem than you realize:
If your old 2 barrel off your 220 is a 500 Holley and has not been re-tuned for your current engine, that is likely a much larger part of your problem than you realize. It is possible in many cases to put that carb on a 472 and get away with it, but unless it was running pig rich on your ground power, it is not supplying enough fuel for you to exercise an early 500 Caddy.radtech wrote:. . . The old 2 barrel that came off my original engine (a 220 GPU) doesn't seem to give the ol cad enough juice and that may be one of the problems. . .
This could very well explain a good part the difference between your results and mine, where coming out of the hole is concerned. There should be no justifiable reason that a reasonably fresh 500 needs to turn over 3k to get on a plane. Quiet has always been part of my quest; I don't think I've ever heard anything turn over three grand that wasn't loud enough to be irritating.
Hypothetically, if it currently has 72or4 jets and a 30cc Accelerator Pump, you most likely would see measurable difference with 76or8 jets and a 50cc pump. IF that IS the case, I would be very surprised if a hundred bucks @ Summit did not provide you with such an improvement that you might not view it as having been band aid. As Slidin Gator eluded to, 500 CFM is plenty of carb in and of itself. I'm just guessing, but if a 4412 is what you have, every indication is that it is internally restricted and is hampering your ability to do what it should be able to do. If it is not a 4412, all the same thought process applies, it just may not be as easy or cost effective to remedy, if it's even possible.
I am not claiming to be any carb guru, but there are some here. If you can identify and share exactly what you have now (jets, acl pump, power valve, etc) you may find you are closer than you think to the performance you aren't attaining right now.
With everything else that's been thrown around in this thread, it would seem logical to me to at least definitively exhaust the possibility before you go to the expense of changing props or spending money elsewhere. I believe you have more performance there to be tapped.