300 I6 is kind of an odd motor to run Duals on. There are Exhaust manifolds out there for dual, but I personally would go Header-Highflow cat-2,1/2 or bigger pipe(3 should be good)-Turbo muffler-tailpipe. If you use this truck for towing or moving a lot of heavy materials, remember, a little backpressure is a good thing to have for torque.