I own a 89 Saleen that I've been slowly upgrading for a track car.  My plan is to upgrade the front end to a Griggs front end.  However, the rear is up in the air.  I read the article about the 92 Fox IRS upgrade but never saw a review as to how it performed after the upgrade was complete.  I've got 450RWHP so wheel hop is a concern, especially on the track.  
QUESTION:  How much and is it worth it?  Kenny Brown parts are hard to come by now so viable replacements or can I still get them for the IRS?
Thanks!