I'd replace all the pickup, lines etc when I cossed 350HP. The stock pickup is the most likely resitriction. If the rest of the stock feed is 3/8 and not kinked or hurt, you could use that. A return system -set up properly - assures that the carb will get the full output the pump can produce. You plub the return into the tank where ever it works for your vehicle. Check the Mallory web site for some good diagrams.