What do those other lines run to?
My 72 Dodge is similar...there are four lines coming out that go into an upright "pipe" that holds the canister for vapors (this was the technology before vapor canisters and other emission equipment). I plan on changing out the tank on my 72 (chop project) and will have to modify with a canister.
This is what that "pipe" looks like in mine.IMG-2336
by Lee Hatfield
, on Flickr