When doing my
swappable conversion, I tried to figure out several of these points, to make them easy swappable. I started from an orignal dump truck with pto-powered hydraulic pimp. Using the original dumb bed, I did not think about the possibilities of putting the hydraulic cylinders on the outside of the frame. D@mm. In the end, I opted for really hard-swapping the bed for the fifth wheel and back because I could not find my way around having both mounted reliable and save and easier swappable.
The main problem for me was the hydraulic pump and hydraulic oil reservoir. For easy removing of the dump bed with the sub frame together, for example on lifting stamps, the problem is that the hydraulic pump is sticking out below the sub frame so the whole unit has to be raised about 10 inches above the frame before you can drive the truck from underneath the unit. Leaving the 5th wheel in place would make that even worse. As side remark, I have a commercial civic 5th wheel on road height, so less high than the original army tractors.
Looking at the drawings (they are GOOD) I still have that question. Where are the hydraulic pump and reservoir located and how is the pump powered? Does it go out with the dump bed or stay mounted?