What parts do you need to rebuild the axle? E-Bay has kits for the transfer case listed all the time and every once in a while you'll see trunnion bearing kits for the front end. A lot depends on the year of the axle; '55 or earlier- very rare; '56 through mid '57- hard to find, but not too bad; 'mid '57 to '59- pretty easy to find. I have a lot of extra parts depending on what you need.
As for power steering, one of the NAPCO trucks I bought had power "assisted" steering. Someone had cobbled-up a cylinder and attached it from the frame to the drag link and put in a Cadillac power steering pump. It was like the steering system on a tractor. I don't know if it worked good, because I never drove the truck. I'm sure a regular system could be put in if you find a power steering gearbox and modify the column.
Disc brakes would be a tough task. A lot of NAPCO owners dream of that mod, but I've never heard of it being done. Good luck on your truck.
Take care, George
