You're asking more questions than I can answer. But, my tailgate is 57" off the ground. Truck is a '14 RAM 3500 dually. I have a Moryde pin box and have raised it to the max to drop the 5ver nose. I'm now level with 7" clearance from bed rails to overhang. Can't answer any questions regarding the short bed. The major variables will be your particular 5th wheel and the pin box. Good Luck.
'14 RAM Longhorn,DRW,4x4,CC, LB, 4.10, Aisin, 70gal underbed fuel tank.
Lifestyle 36FW, 8000lb axles, disk brakes, 19,100lbs
Andersen AL Ultimate hitch