My 79 4x4 was sloppy like that when I got it. My brother borrowed for a day when his truck was down. He never borrowed it again.

He said driving it was like "pushing a cow on a rope". Most of the slop in mine was the idler arm bushing though. The steering box was (still is) only a minor part of it. Greasing the idler arm on these trucks is a challenge so they often get neglected. From my experience it seems to be a common problem. I've rebushed the ilder arm on all four of the LUVs I've had as drivers.
If you have not already, get under the truck with a friend in the cab turning the wheel back and forth while you look. Make sure your problem is all in the box and not elsewhere. If you get your helper to turn the wheel slowly back and forth just far enough to move the tires a nudge, then you can feel each joint as it moves and see how bad each one is. The ilder arm should just pivot with the shaft, but when it is worn out the shaft will wiggle back and forth before the arm moves much.
You can also take a crack at adjusting the lash on the box itself. I've never done it myself, as I usually found more to fix elsewhere (like idler arms) but it looks pretty straighforward. Loosen the nut on the box, turn the screw. The Haynes shop manual describes the process pretty well and is well worth the $12-15 if you don't have a shop manual already.
As far as swaps go, you might find that an Isuzu PUP or early (84-85) trooper manual box will work, though I don't know how many of them came without a power steering setup. The 83 PUP I used to have was, but it was 2WD, and probably different (at least the arm) from the 4WD setup.