When I was hauling RV's commercially I had a friend (mechanic) found me a Mercedes diesel with 5 speed out of a box truck. It would have had about 50 more HP than the Chevy diesel. We had measured everything and it would have been an easy fit (without shoehorn). And reasonable to rebuild. This was going to go in my Chevy dually but the first gulf war struck and the RV business went right out the window.