Very nice work buggyman. I was close to doing the same thing but went ahead and bought an M817 (in-op). Yours goes to a large enough angle to get rid of a very sticky load. That's good.
TommyFrantz, yes you can save a lot by having the PTO, pump and valve in place. You will have to add some additional items like a larger tank and a double valve OR put in three way that controls which gets flow...winch or dump bed. You can also do it with stack valve and 24 vdc. In fact an open center 24 vdc could be used to change the flow and you still would use the winch handle for up-down.
I have a 925 that I will be doing that modification to at a later date. But I will probably use a single telescoping cylinder at the front with some bed modification. I'm trying to determine if I can fabricate a knuckle boom as a center mount. Note you better plan on reinforcing the skin of your bed as it will dent easily.
EDIT...If your purchasing a scissor unit, look into a unit that has a double pivot. They increase the lift capacity at the critical start point and I don't think cost any more than this style.