"third nipple" on fuel pump?

[63burban4x4]

got a low milage 350 from a 1986 c-60. I never saw it in the donor truck. on the bottom of the fuel pump has a "third nipple" between the inlet & the outlet nipples. this had been plugged with a short hose & clamped-in bolt. looked as though it had been run that way. truck had a governed 2 barrel, will now have q-jet on a '66 stock intake

anybody know what this did?
can I just plug this (a bit more elegantly), and be done with it?

[hjewell2]

I would say the plugged port is a fuel return line. yep you can plug it off