I put an 03 IRS in my 97 Cobra and love it. I don't auto-x it but I open track it. Here is what I have done with it. MM urethane IRS bushings and a-arm bushings (upper and lower), Aluminum front diff bushings, delrin rear diff bushing, MJ's/Billet Flow's diff brace, 4.30 gears, bilsteins with MM coil overs at all 4 corners, 03 Cobra drive shaft. There isn't enough adjustment to get the amount of negative camber I would like for the track. I am thinking about custom a-arms with rod ends for that reason. I still want to ugrade to DSS level 5 half shafts.
As it is it works real well. By all means do the bushing while you have ithe IRS out already. They are a major pain in the butt to install.