I kinda know what I'm talking about when it comes to 7/9 suspension. I'm very familiar with this issue. Even new shocks and springs will not cure it, it may help mask it. The worn bushings are allowing the axle to move in a way that can not be restricted by springs and shocks. This makes for some unpredictable weight transfer when going over a bump while cornering.
Replace the torque arm bushing with poly, or a solid unit like what Kaplhenke sells. Do they make replacement pan hard bushings? I just got a replacement PH rod with heim joints.
If you're beating on your car, you will need to consider reenforcing the subframe connector. Yoshifab has a good budget weld on kit, and Ben sells a high dollar replacement. At least inspect the subframe connector when you are replacing the bushings so see how worn and bent it is.
There really isn't anything else to say on this issue. Spring and shock talk should be in another thread, it's not going to fix this particular issue, it may mask it, but you're still going to have a floppy rear end, and no one wants to rock a floppy rear end.