The IRS reduces rear lift under braking, making driving the Cobra hard a much more forgiving task. It improves the vehicle's attitude and control, with a full 0.75 ins. (1.9 cm) more suspension travel available. And it reduces the unsprung weight of the Cobra by 125 lbs. (57 kg). As expected, the IRS carries with it a fairly stiff weight penalty. To help compensate for the system's extra 70-lb. (32-kg) heft, SVT engineers extracted close to 50 lbs. (23 kg) from the car. The result: a weight distribution that moves from a 57%/43% front-to-rear split in the 1998 model to 55%/45% with the 1999, a significant enough amount to equal the effect of moving 80 lbs. (36kg) off the front wheels. Ford didn't limit its tweaks to the rear wheels, however. Besides the addition of the IRS, Ford also addressed other aspects of the chassis to improve the car's handling characteristics, like widening the rear track by 1.2 ins. (3 cm) to match the space between the front wheels and lowering it overall by 0.25 ins. (0.6 cm).
However this is the only photo I have that shows the two setups side-by-side so someone can really get a feel for all the parts that make up a complete IRS. Please feel free to rip the IRS out of your '01 and then get a similarly equipped 8.8 and set them side by side for a better set of comparison pics. 
