I saw a AD COE with a Dodge Cummins mounted behind the cab, he had a bed around it, and a cover something like you would expect for an inboard boat engine, a lump sort of with doors made of aluminum sheet with louvers punched in it, it looked ok, but nothing special, and just about made the bed useless. As for having the engine behind the cab I think he did about as good as he could for having a useful and good looking truck, but it still looked weird and out of place..
What's wrong with an engine under the cab?
Grigg