I ran a new 1/2" (I think) SS braided line for the supply and used the original supply line for the return since the original return line is too small for all but the lowest HP applications for a F/I swap. I ran the new braided supply right on top of or next to the old supply and used short pieces of rubber hose spaced at about 12" intervals to keep it from chaffing against the original line then used plastic ty-wraps to hold them together.
Rather than connect the original supply to the return port on the tank I decided to attach a length of rubber fuel line to it and run that over to top of the tank and use the vent on the top left corner of the tank for an inlet port. That port was bigger on my tank than the original fuel return port. The old return line is still in place in case I want to return to original.
Since your tank is out, I'd just get the original return port replaced with a 3/8" and run the original supply to it rather than mess with the vent. Leave the vent functional.
good luck with it
[edit]
Oh yeah, I also meant to mention that I went with an external Holly fuel pump and pre-filter that I got from the Summit catalog. I get about 2 years of daily driving use out of the pumps before they die. They start getting increasingly noisy right before it'll leave you on the side of the road.
If you don't mind spending some extra money on tank mods I'd suggest an OE style internal fuel pump. It'll be quieter and much more reliable.
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