You can get used orbitals off forklifts and other equipment that may or may not work right-there are 100's of different ones that look the same. Plenty of options for new/used hydro cylinders. I've had better luck out of stock pumps than psc/pos. Several people I know use log splinter valves for the rear steer.
You are gonna have to spend time searching to find out what will/will not work, or trial and error.
the one that we did we used 2 stock power steering pumps an orbital valve off of a forklift and a log splitter valve for the rear. One pump for the front and one for the rear. works great