IRS into Fox body

[Northstar]

I have a 1979 Mustang and would like to upgrade the rear suspension to the irs from a Cobra. I have been watching Ebay last couple of weeks and so far it seems the 03-04 would be the best with the 31 splines. What other differences have occurred to the IRS over the years?
I thought of buying just the frame and pick up parts as I go. I see there are components that should be upgraded. I am not going to drag race just crusing and possible some autocrossing.

[InfamousSVT]

First off, welcome to the boards!:thumbsup:

The 03/04 Cobra IRS is the strongest "factory" halfshafts made, which are 31-spline rather then the previous 28-spline halfshafts.
Since you don't want to drag race the car and will be using it for mostly street and autocross the IRS will benefit you greatly.
The upgrades to the stock IRS are just basic really. The rubber bushings all need to be replaced and then you'd want to get a IRS brace, like that from Billetflow.com other than that it's pretty much safe depending on how much horsepower you're putting to the ground.
You can probably pick up a stock one for around $1200, but if you keep an eye out you may find one with the bushings already replaced, cause those are a PITA to do:D

[Northstar]

How necessary is the brace I have seen for the rear cover? Any articles out there on beefing up the rear end? Like in different stages.

[InfamousSVT]

Basically, just get the IRS brace and some urethane bushings and you're good!
As long as you don't get wheel hop, you won't have any issues breaking anything!

Guys using the Billet Flow IRS brace have been at the strip dumping at 6krpm without any problems..........now if you didn't have the brace, you'd be picking up your rear-end all over the place:D