Non Mopar carburetor opinion

First off, I would like to thank any of yall in advance for offering an opinion. I put a lot of time into trying to help people and time is valuable. That said, here is my question.

1975 Ford F250 Camper Special. 351M (I know, it's a transplant) T18 4 speed, Dana 60 with 3.73 gears.

I am SLOWLY working on building up a .030 over 400 Ford engine. It will be mild. 9.4:1, smallest Thumpr hyd roller cam 227 241 @ .050, on a 107 LSA. Will run headers.

The 351M now is not quite stock. It is except for the cam. I measured lift when I had to do heads on it before Christmas. Looks like it is the tried and true Melling/Sealed Power/whatever 204 214 @ .050 .484 .512 lift. Lift is tall cause of the 1.73 rockers. It bumps slightly when cold and almost not at all when warm. Running manifolds right now.

Has a Holey 4175 650 spread bore vacuum secondary. No choke. I live in Georgia. Weiand Action plus intake, I plan to use it on the 400. Also have the GM style HEI distributor.

Here's the deal. The carburetor "runs ok". I could never get the air screws just right. If I tighten them up all the way, it idles up a little. Like they cannot go in far enough. It HAS popped through the carb some trying to tune here and there. Might have got the power valve.....but IMO it runs too damn good. Probably anybody else but me would be happy with it.

I know the 400 will probably need something different/better/bigger/whatthehellever. So here is what I want to do. I would like to try one of those new Street Demon 3 barrel jobs. I want to do it before I swap engines, because I know there is room for improvement.

I feel like the 351M would probably be best with the 650. I think though with the 400 (they are actually 402 stock .030 over it will be a 408 ), that it will be better with the 750 considering the mods I plan. I also plan to ditch the M block heads and use the better flowing early 70s 351C 2V heads and headers on the 400.

Do yall think the 750 will drown the 351M now? They are like a TQ in that they only flow what the engine needs, but I am worried the primary side might be a little rich. So whaddya think?

Oh and there's this also. Right now, the 351 will suck the 650 for all it's worth if I stand on it. It runs very strong for a probably 7.8:1 engine.