I'd just upgrade both rear bars w/ some tubular ones from either GMPP or the like. Since the bushing will be stuck in the part where it attaches to the body mount bracket I'd replace that too. You can still buy a new bracket, nut and bolt from any GM dealer. I just did this on my 00 GT and installed all new brackets/hardware. Made life much easier and only cost about $35 total for both sides. After beating on my old ones for over an hour trying to remove the stock arms I just said f it and went the easy route
The rear bolt that goes through the hub assembly will likely be seized w/ corrosion due to it being aluminum. Just use some PB blaster and work with the bolt. It'll come out.