Does the tire rub because of it's height, or it's width??? If the tire is too close because of the tire's height, you could just raise the coilovers a round or two...If the tire is too close because it's too wide, a different backspace wheel would cure that. Whichever solution cures it would be much less $$$$ and far easier then switching rear ends.... Going from a Jag IRS to a Quicky would require some serious mods to the rear frame plus the cost of the quick change itself!!!