I restored a 4000 once that had PS. The pump was shot so rather than buy an OEM pump, I went to the auto salvage yard and got a pump from a car and used that, building the suitable adapter.
The problem with it was that the flow rate was too low for a tractor with 2 pistons and a pto speed at 1600. It took forever for it to turn and after awhile, I just took it off. I couldn't change the pulley ratio to speed it up as it was driven off a double chev and the other slot was where my fan drive was hooked up.
Soooo if you cobble one together, get one with a suitable pump volume.