Holley 6709 double pumper 750 carb info

So some of the questions I'm thinking about these weird carbs are, 1. can these carbs have that backfire check ball protection installed? 2. I've herd they don't flow what they should. is that a good thing? cause together their possibly to big for my 451... 3. I saw something about these in a dual quad circumstance, what kind of power valve arrangement and jetting would these weird things run if they were on a tunnel ran? Or would I be the first person to try these puppy's as a dual quad