I'll second or third the idea of central hydraulics or depending on the tranny, you might be able to run it off that. With central hydraulics, you will also be able to control the conveyor or auger and the spinner independently. This is very important, IMO. Our's is the Allison World tranny, so the pump is powered off the tranny, once winter hits, it is shut off only when we park it when finished.
I could be mistaken, but I believe that there are pumps designed for different engines--gas, higher RPM's and diesel, lower RPM's. If the pump and the plumbing to the pump is already there, it shouldn't cost that much to switch out the pump for one that would work.
LGF, hard to say, our F750 flatbed w\10' spreader weighs in at 18,000 even. Leaves us 15,000# for salt and we use it. I realize the hook is going to weigh more, so that will reduce the capacity somewhat.