[750hp]

If your only current problem is down to the quality of filtering on your inlet side, then I'd keep the webers (and fit a large filter that can go down to 4 or 5 microns). If you are still having driveability problems that are tuning related, then I'd flick the webers and try a single plane manifold. It seems like the only problem that you've been having with the Mustang is always related to these damn webers. I'm kinda surprised that you have had such patience with them.

Do you get on OK with the local mustang club? Surely someone there will have a manifold and carb lying around for you to try. For the sake of a set of intake gaskets, I'd do it - if nothing else but for you to know what each intake combo feels like. I would suggest that a 750 carb - either vac. sec. or DP - and a Vic Jr manifold would make more peak HP for your combo, and be a true "set and forget" tune-up deal. You may lose a little lower range torque, but not enough to be a concern.

What trans are you using again?
Diff gears?
Tyre size?