Sig, it's not just the fuel pressure, its the volume needed to keep both float bowls full. Empirically, at 6-8 psi (Holley fuel pressure range), it takes a 3/8" or larger OD line all the way from the fuel inlet inside the tank, to the later Holley float bowl needles.
With EFI at 55 psi, the stock 5/16" OD line will flow enough to work. TBI runs at about 12 psi and such electric pumps can be regulated down to 6-8 psi for Holley carburetors. But if you try regulating a high-pressure EFI pump down for carb use, the restriction is so large that either some models of e-pump's thermal-reset breaker will trip, then a few minutes later, will reset. Or in other e-pumps, there's an overload wire inside the pump that will burn through. Such pumps are then junk. Ford 12 psi TBI pumps look identical to Ford 55 psi multipoint EFI pumps and may not have markings, so be careful with used or bargain pumps.