If you eventually go with EFI you probable need a return line to dump the extra fuel from the high pressure pump. You could install the high pressure pump on the regular line in the tank, use the new return line for now with the low pressure lift pump and just rig the plumbing in the engine compartment to use either line as needed.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy