I do not know about your 1970-LS-5. My LS-5 has the two line fuel pump.
Why the two line fuel pump? It ia a vapor line FROM the tank. In 1970 the 454 Chevelle had a " 100% " CLOSED Emission System ". WADDA, YA mean?
ALL--Engine fumes--Fuel Fumes--Were entered into the engine and after the fumes & Emission gasses were burned off,, They would EXIT the tailpipe.
The fuel tank fumes on my 1970 LS-5/M-22 El Camino are vented into the 1/4" steel line at the fuel tank and then are pumped ( via, two line fuel pump) into the 7040205 Q-Jet to be burned off and sent into the atmosphere, VIA the tail pipe.
If you look at a correct 70-454,,, Engine fumes from the left side valve cover......... Where do they go?... Right side valve cover, Where do the fumes go? Also, Some 70s had Charcoal cannisters, Located engine bay, behind seats,.
Also: Do you need to operate you engine with the two line fuel pump, " NO ". Just so you know... On my FAKE//FRAUD--1970 SS 454 Sta. Wgn. I have the O.E.M. , long cannister fuel pump, WELL, What about the 1/4" vapor line?? So my FAKE SS looks real... I got a piece of brake line about 8" long, I soldered the end shut, Attached a piece of 1/4" fuel hose to the pump and then stuck 8" piece of 1/4" steel brake line with the end soldered shut, And stuffed it into the frame beside the stock 5/16" fuel line.
So when you look at my FAKE LS-5-SS,,,, BUBBA says,,, YEP its a real LS-5,,,, Its got the two line fuel system.
Its the joke about the " Book & Cover". In the early days of the " NEW EMISSION SYSTEMS",,,, Late 60s & Early 70s---- G.M.--Ford & MOPAR were ALL OVER the place with emission equipment !
The beginning of the end is near with " Horsepower "--late 60s & early 70s...........
P.S. Fifty years ago this month, I ordered my LS-5/M-22 at Sahli, Chevrolet, in Beaver Falls,Pa. The second week of March.. It will be " 50 " years old.