i remember reading a few months back in a 5.0&SF mag or MMFF mag about some fox's with the cobra IRS set up...i'm sure anything is possible if you have the know how...i haven't seen anything about using an '01 IRS specifically...i'm not sure if those are wider or not or how much of a bolt in it would be...but if you're getting a good price on it i would say snag it regardless. the 2003 cobra IRS set up is priced upwards of $2,600 new from ford racing according to the '04 catalog...so if you can get it cheap, grab it...you could always sell it.