Depends which fuel pump module that you are using. If you use the Holley muscle car module then you don't need a return line. Holley makes a 350 LPH internal pump module which supports 700+ hp and it doesn't need a return line since the return is in the tank. It also doesn't need a regulator since the regulator is in the tank. Just hook up your existing line to the new pump and you're good to go.
