If you purchase a used rear axle to install in your car, it may well have worn upper control arm bushings. Shown below (left) are the bushings that came with the used 8.8" axle I purchased. The rubber is split, and the central shafts have been knocked off center. On the right are bushings I removed from my stock 7.5" axle. They are in very good condition. I'll just swap them out.
Ford uses a special tool (below left) to remove/install these bushings. Maximum Motorsports will sell you a tool (below right) that does the same job. It comes with very complete instructions on its use. The MM tool costs $40 plus shipping. The way I figure it, that's considerably less than I would have to pay a mechanic to do the job, and I get to keep the tool. (I've bought a lot of tools that way...)
You also need to buy some anti-sieze compound, which is required for the threaded special tool to work smoothly.
Support the body and the rear axle on jackstands so that the upper control arms are not stressed (1). Then unbolt the upper control arm and push it aside (2). So long as you only unbolt one side at a time, the control arm/bushing will stay lined up, and reinsertion of the control arm bolt will be easy.
The special tool is used to remove the old bushing (3) and leave just a cast iron ring on the axle housing (4).
Then the same tool, slightly reconfigured, is used to install the new bushing (5). Ford specs call for the bushing to be installed so that the bushing lip is 36mm from the back of the cast iron ring. I checked it and found that the MM tool installs the bushing to exactly that spec. (6)
Bolt the control arm back up, then do the other side. That's it.