Unless you buy a function built external tank, it is hard to have a stable fuel system. Fuel sloshing from side to side can starve the fuel pump on a sump fuel system. Aermotive has come out with a new weld on sump kit they call the "Stealth".
Inside the sump includes your choice of a A1000 or Eliminator fuel pump. Also inside is a pre-filter and a cam lock cover that allows you to service the pre-filter without draining your fuel tank.
The pick up for the pump sits a fraction of an inch from the bottom of the sump, which only requires only a half-gallon of fuel to operate properly. The fuel return is opposite of the pick up to keep the warm fuel from being pumped back into the motor. For Fox body applications, Aeromotive includes everything from the fuel cell to the rails, with all fittings and lines.
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http://www.aeromotiveinc.com/ for more information