If you’re going to buy a whole 750 to use with that Proform body, make sure it’s a new enough one that already has 4 corner idle.
The older 4779’s didn’t have it.
I don’t know what dash number it was when the 4 corner idle was std.

I can’t quite make out what your stock main body number is.
4777-7?

That’s what I used to make my dyno carb out of.
I’m not sure what vintage the metering blocks are, but I believe they’re earlier than a -7 though.
They have the emulsion tubes in the primary block....... but if you’re working with a matched set of components from a 4777-7, then it would appear they had done away with that by that the time the -7 was made.

I used an aftermarket base plate, and modded the rear metering block and main body to have 4 corner idle.