mech. fuel pump variation

[longbedrick]

installed a fuel pump on a Big Block '69 El Camino a while back, and noticed there was (1) inlet and (1) oulet on the mechanical fuel pump. On my '73 Big Block 454 it seems there are (2) inlets and (1) outlet. Why the variation? my truck has dual tanks. there are 3 ridgid lines running from the two tanks. (2) lines to the pump, one line to the charcoal canister

Here's mine on the '73