Choosing A TB For A Magnum

The size of the TB has little to do with it. You are not trynna produce vacuum signal as with a carb

Biggest thing I think with NA EFI is "ram length" IE manifold design, runner length, etc.

The old Holley TBI on my 318 is 950 CFM 4 bbl!!!

Too small and it will act like a choke at WOT

"Really" large and my perception is that you get into a control problem, IE you move the throttle a tiny bit (slow street driving in traffic) and "that great big throttle" opens by a large percentage for a small input