A stock 5.9 Magnum IS the 300 hp 360 crate motor. Check the part numbers. Cam, crank, heads, and everythign else is the same. Add your own intake and go.

Get a 5.9 Magnum. Add a carbed intake and electric fuel pump. Hit the road.

If you want a little more pulling power, you can swap to an RV type cam but that's optional.

If you really want torque, swap in a real 5.9 (read: Cummins) and drag all the gassers sideways.