The fuel pressure of a TBI isn't that far off for a carb.Well really it is but not as bad as a CPI 4.3.Keep the in tank pump and get a regulator that has a return line on it and put a fuel pressure gauge in line under the hood to set the pressure.You use the 4.3 return line like it was on the 4.3.

You know just a thought.Your saying the engine came out of a EFI truck.Was that also a TBI??. With that you might have some other options.