Fuel line question

[Hair]

I have a 71 GMC that came with an I6, putting a 1988 carbureted 454 in it. I am in the process of hooking up the fuel lines to the pump. The pump has two lines out the bottom and a connection out the side which goes to the carb.

My tank has two lines coming out the bottom thru the cab floor:
- One runs up the frame to the pump, I'm sure that's my fuel delivery line.
- But the other line is a rubber hose about 12" long and it is just hanging back there under the cab. Looks like its been hanging there like that for years.

Question: Do I need to run that other line up to the pump and hook it to one of those tubes out the bottom of the pump?? Or do I put a nipple on one of the pump lines to plug it off, and just leave that old hose hanging back there, maybe its a vent or something??

Also, concerning the two tubes out the bottom of the pump, does it matter which one I hook the fuel line to??