I just installed new poly bushings all around on my 87 Z52. The front bar is 30mm and the rear is 22mm.
You may want to swap the front bushings at the same time if you are considering poly bushings. New bushing in the rear only will change how the car handles. The end link bushings should be done at the same time. A complete set of poly bushings should be around $50-$70 and figure up to around $50-100 for labor to install the end link bushings.
When I did my 87, I found a lot of rust on the nuts and bolts that hold the bar bushings to the body. You will have to remove the spare tire carrier (easy!) to get to the nuts and remove the bar from the car. Be ready to soak the nuts with WD-40 or equal. One nut did not want to turn because of the rust and I was afraid I would snap the bolt which is pressed into a bracket. After about a quater can of WD-40, it started to turn but got really hot! All of these nuts are 13mm, so make sure you have 6-point sockets. The nuts on the end links are 18mm and the bolt is 15mm.
I cleaned up the threads with a die and used all new nuts and some anti-sieze compound for the re-install.