Gas tank conversion help needed

[revitout]

It has had twin tanks in before by the guy that built it. There is nothing left apart from the holes that mounted the side gas tanks , and one feed fuel line running up the right side to where the mech fuel pump was. I have been doing lots of reading and think I need mech fuel pump with no return and 600 Holley. Just wondering if I need 2port sender and which selection valve , and what powers it , 12v or vacuum? I can't see any trace of wires etc or where it was located before being stripped out and lpg system installed.