Since the IRS control arms can be set up just like an independent front suspension, it can be manipulated to keep more tire contact at more angles than a straight axle unit can be.
With the proper geometry, it can also be manipulated to increase corner turn in toe and camber, which can be very important on road tracks- not so much for drag racing or street. Since there is less unsprung weight, road manners are also better, especially on rough roads.
The 8.8" Ford is a very nice IRS to use and work with, but many others are available that can work equally well. I believe the Jag Rears are available with outboard rear ends on some kits. The Everett Morrison takes Vette suspension, including IRS IIRC. Some kits are available with Ford 9" adapted IRS set ups and several aftermarket companies make 9" Ford IRS set ups for many applications, but I'm not aware of any distinctly made for a Cobra. However, anything can be made to fit with enough work.
Most IRS can be made to handle substantial amounts of HP/Torque with the proper hardened and machined axles. Several aftermarket shops make high torque rated axles/CV's for the 8.8 Ford IRS as well as the 9" Ford IRS units.
Try
www.dutchmanaxles.com for one place for 9" Ford IRS set ups and custom, race rated axles. Very nice work, good people to deal with, and very good service. AMP also offers these pieces but their reputation for service is somewhat "lacking".
If anyone is looking for one, I happen to know where a Jag Rear and front suspension out of a Contemporary is available at the moment. Includes Wilwood brakes, inboard brakes in rear, and all the suspension pieces.
Bob