Dont get poly bushings! Just go to the parts store and get a set of Moog replacement bushings. These are great quality and are stiff enough to give good responce but soft enough to give good ride quality.
Here's what your problem is or a combo of them in all reality:
1. You cut Monza springs down you said, are these progressive rate or solidly sprung? If they are progressive rate and you cut them, you are essentially riding on wabbly springs. Thhe solid srpung direct rate springs when cut are too stiff to allow weight transfer to the rear wheels so the engery is now wanting to exit through the control arms which will cause hop.
2. old bushings, usually in the rear end itself will allow vibration to pass through at an expanded rate so instead of putting the power to the ground directly, it's now distorted as it transfers energy from the body through the rear end and then again through the lower control arms and back into the body. Most of the time the probelm isnt the lower control arm bushings though, its the bushings perched on the top of the rear end.
3. Your pinion angle is completely out of whack lowered 2" with non adjustable upper control arms. If you want to be low, you need to buy adjustable uppers. Dont mess around with the relocation brackets for the lower control arms unless you cant get you pinion angle with adjustable uppers alone, which trust me you will. The relocation brackets are just another part bolted on that will have the tendonsy to flex.
Solution, buy a new set of springs even if it raises the car 1/2". I like Moog 5413's, BellTechs, or Global Wests which will sit the car 1.5" lower. See how it reacts and if it still hopping, get a new set of bushing for the perches on the rear. Still Hopping??? double adjustable upper control arms to se t your pinion angle. Still Hopping?? change the lower control arm bushings or get a good set of Hotchkis or metcos.
What are you using for a rear swaybar?
