the pump, brackets and hoses are fairly easy to come by, and the pulley isn't too hard to find either. new and used boxes are out there, so that's not a huge deal. you can reuse your pitman if you find a small sector box. otherwise the 73+ power stuff used the large sector.
the fly in the ointment is the column length. the housing is the same, but the manual steering shaft is ~40.6" and the power shaft is shorter at ~37.5".
so you'll need to either cut the shaft and run a u-joint adapter (or weld the old bit back on), break the locating pins in the shaft and slide it up further or source a new inner shaft (or complete power column).
the coupler, that box thingy that connects to the steering box is also a different size between manual and power, so you'll need one of those.