I just recently installed a 2003 Cobra IRS in my 95 cobra.
It bolts up except for the following issues....
1) The rear IRS subframe mount is designed to have 4 bolts, two horizontal, two vertical. The 99-older cars DO NOT have holes for the vertical bolts. Because of this you will either need to get the rear subframe mount welded to your chassis, or drill through the frame rail, get long bolts and bolt it down.
2) You will need to make new hard lines for the rear. Just buy a brake line T from the local auto parts store, buy some hardline and bend away.
3) I *think* that you need to use your stock 95 e-brake cables.
Other than that it bolts in.
Also, while it's out you might as well add MM IRS subframe bushings, these keep the IRS subframe from shifting around. This will help prevent wheel hop and improve handling. Lastly, adding an IRS pinion brace and pinion bushings will help too.