Any pump will just about do but a small pump or even PS pump will have lower volume and take a while to stand the dump box up. The pump I have on my crane is rating a little over 2000PSI and 25-28GPH and the crane moves with good speed with that. The mast raises with speed and the boom telescopes with speed as well, I use those two references as they are pretty decent sized rams like the dump will have. I'm using an older Commercial brand pump somewhat similiar to what Cranetruck has on his. A nice healthy gear pump will do you fine. Again, any pump will pretty much do but higher volume will mean faster lift rate. Oh, something along the lines of a 7/8"- 1-1/8" keyed shaft will make PTO drive parts easy to find/build. Tractor Supply or the like will have a good supply of U-joints, couplers, sprockets, etc.