Hey I have a power steering conversion done to my 1st gen. The box just bolts right in. You can use pretty much any Mitsubishi power steering box of that era - 1st gen Pajero/Montero should be the same, 2nd gen mighty max, Galants etc.
The box body and arm is all the same, its just the top section that's different (its actually shorter which is why it was done to my truck to clear the exhaust manifolds on the v6), here in nz a lot of the 2nd gen trucks were power steer and that's where my box came from

I cant help with the pump as my engine is not a Mitsubishi. , I would imagine you can use the 4wd one with out any issue