I put a MAC catback on my 98GT with no issues. Maybe because no IRS? I had BBK ceramic long tubes, off road H pipe, and the MAC C/B - it sounded ridiculous! I got compliments on the sound where ever I went, the long tubes were a **** to put in (not that I'm telling you Modular folks anything new) On my 03 Cobra I have stock manifilds with a pro-chamber and the Magnaflow C/B; it doesn't touch the sound of my GT but it does sound OK. I think I am going to do the MAC cat back again - I want some bass back!