magnum power steering pump with serpentine belt adapted to 73 power steering box?

You probably should supply more info on his plan, as there are other difficulties with this setup. The narrow engine compartment causes battery tray clearance issues with full size pickup truck power steering brackets but not usually with van brackets. Also, if he is running a carburetor, the factory magnum timing cover does not have provisions for running a mechanical fuel pump, and a magnum water pump won't work on a LA style timing cover. All easy fixes, but make sure he knows before buying parts.