ive read this thread fron to back. i would suggest 3 things to fix your problem if you stay with the springs you have now. 1) change tire size from 60 to 50. this will give you additional room in the wheel well opening as far as height goes! 2) increase the shackle bracket length. you can increase the length by 1" to help wiht the problem. you will no longer be at stock heigth but it will help with rubbing when going over bumps.
3) nchange the rims to a better back spacing. i will argue with anyone here when it comes to having this large of a tire on our birds. i have 245/75/15 on my car now for an example and have a few inches to play with. i know this isnt the 275 size in question but it is close! im sure it will accomidate a MUCH LARGER tire size when i go to it! you can get a better idea of the larger sizes and backspacings used on the camaro forums. im not into modifying metal to make it work sohe backspacing HAS TO BE NAILED for this to work. were talking 1/8" increments here!

you might also try stiffer shocks as a fourth alternative!