I have changed the box and the rag joint in my car, as the well as every other component in the steering and suspension (the only things I haven't removed were the dash pad, doors and fenders). It is quite helpful to have the shop manual for this job, as it helps in rebuilding the control valve. Another thing that makes this job easier (you don't have to) is to remove the hood, before jacking the car up. This will give you lots of room to work, and let in plenty of light. Just make sure you mark the location so the hood goes back in the same place.
Start with the rag joint, just turn the steering wheel till you can get at the bolts, and loosen the clamp up, this is it no big deal. When the rag joint bolts are loose, just center the steering wheel so the tires are facing straight.
If you have power steering, the worst part of the job is separating the ball stud in the power steering control valve from the pitman arm. There is a special type of ball joint separator that is needed which pushs the ball stud through the pitman arm, the problem is there is not enough room. Some guys I know have have been able to separate this by banging the pitman arm with a 2 pound drilling hammer to unlock the taper, but this didn't work for me. Since I was rebuiling the entire system, I just used a pickle fork to separate the ball stud from the pitman arm. This will rip the ball stud out of the control valve. My control valve had 260,000 miles on it and I was going to completely overhaul it anyway. I was not thrilled doing this, but if you are going to put a new box in, it is time to rebuild the control valve, and the slave cylinder anyway. I had bought a rebuild kit for the control valve and a new ball stud, all the parts are available through the Mustang parts house, they come with all the instructions you need, are are not hard at all to do. Even after the hack job I did to remove it, after the rebuild it works perfect, have no fear. The slave cylinder was easy to rebuild also, and now there is no leaks.
Now with the rag joint loose, and the the pitman arn separated from the control valve, you just remove the 3 bolts that hold the box in. When I did this job, I think I had the power steering pump removed, so there was room to get the box out. With the box out of the car, before removing the pitman arm from the box, you must take notes on where the arm is in relation to the center steering position, so the arm can be reinstalled on the new box in the correct location. I believe the end of the box that goes into the rag joint has a hash mark on it for referance. You will need another type puller to remove the pitman arm. Once this is done you can knock out the old ball stud from the pitman arm. When you install the pitman arm on the sector shaft of the new box, it is to be torqued to 150-225 foot pounds. I was only able to torque it to 150 ft lbs thats alot of oomph, believe me.
I had used a polyurethane coupler (rag joint) as all of the bushings in the suspension were done in poly (she handles like a slot car). Why spend the bucks on a new box, and have a sloppy coupler. The poly kit comes with only bolts, and you will notice the stock coupler has 2 different size locator pins. Now I don't know what kind of hardware the stock (sloppy) couplers come with (hopefully correct, if they come with them) but I cut the old pins and tig welded them back into the poly coupler. I believe the stock 2 different size pins will push into the stock coupler. I didn't like the idea of a 1/4 or 5/16 bolt being in a 5/8 or 3/4 slot on on one side of the coupler, as the pins would not push into the poly unit. I am quite sure this would not be a problem, because the other side will fit tight with the bolt instead of the pin. I am just anal retentive and have access to a tig welder. I know from reading this you have no idea what I am trying to say, but once you remove the coupler it will make sense.
When you put the box back in, make sure the box is centered and so is the steering wheel when you connect the coupler to the column shaft. Another thing to remember is when you remove the control valve from the center link for rebuilding, count how many threads are left exposed on the center link and take note of it. This way after you rebuild the control valve, you can get it back in the correct position to connect to the pitman arm. Now button everthing back up, fill the P/S pump up with fluid, purge the air in the system, and off to the alighnment shop. Then you can truly enjoy what the steering is supposed to be like, you will be amazed.
I hope this answers your question
Jay