I thought I'd answer the question about how difficult it is to remve the box. Plan your self some time is all I have to say. The most difficul part is the sterring wheel, there is a post here about reuilding the box in place but I found it a lot easier to remove it completely. You will need steering wheel puller, so invest some time in that. Once the wheel is off it gets pretty easy, remove the drag link from the pitman arm, remove the collar on the column at the dash, then remove the three large bolts that hold the box to the frame, by lifting, and rotating the assembly you can pull it right out from the front, I would reccomen taking the front fender off before you do this, makes it a lot easier.
Now for the fun part, there are kits you can buy to rebuild the entier box, but as long as you are at it, I would buy the parts to rebuild your drag link, bell crank and tie rod ends, and I would also include a "Tight Steer" as well. You will be much happier if you do all of this than if you just pick at it. Spoken from experience.
The "Jeep Universal" manual does a good job of walking you through all of this, so good luck.