I saw earlier on Monster Garage, Jesse and his guys ripped a Cummins N14 out of a 70's Peterbuilt and used it as the frame for a tricycle. They connected via u-joint the semi's rear axle directly to the transmission, and fabbed a single wheel front end for it. The driver's seat was situated to the left of the engine, in sidecar fashion, and they even mounted the exhaust pipe so as to blow all the sound/soot directly into passing motorists' windows. It used a belt-driven compressor and an air tank to operate the air brakes and to retain the Peterbuilt's horns... It looked slightly difficult to shift, but was totally awesome!