Does your FJ73 have P/S? As long as you have the complete kit it will be ok.
(I plugged a HZJ75 pump and hoses into a FJ73 steering box and it worked like it was there from the factory)
You say the parts are from "an old FJ75" The pump could be 22 years old and be in need of a rebuild.
If you have any problems I have pics of my FJ73 P/S pump and brackets,in fact I have the whole set up