1987cut

Hey guys, i'm in need of some help. I'm currently installing my 99 ls1 into my 1972 c10 pickup. Im going to run the stock ls1 tank/fuel pump combo under the bed. I was told this is a returnless system. I'm wondering how to run the fuel lines from the pump to the fuel rail. What about those other two nipples on the tank? any help would be greatly appreciated. thanks