That rotor is a 93-97 Tbird/Cougar rotor. You can see someone ovaled out the lug holes to be able to run it on a Mustang bolt pattern, which is what I assume you have on your Cobra. If you have the Mustang bolt pattern, then you could have gotten that in one of 2 ways. Either someone swapped in 99-04 Mustang Cobra rear hubs, or someone re-drilled the T-bird rear hubs. Basically if you have an extra set of holes in the hubs, then they are Tbird hubs, and if there are no extra holes, then they are Cobra hubs. If you have re-drilled T-bird hubs simplest thing to do at this point would be to oval out the holes on the new rotors. However if you have Cobra hubs, then you have another issue to deal with, namely the hub center bore is larger on the Mustang, so to use a T-bird rotor you would also have to enlarge the center bore. If you want to run actual Mustang Cobra rear brake rotors, you need to either make or buy a set of adapter brackets. You can retain the T-bird caliper, with a relocation bracket that moves the caliper away from the centerline of the axle to deal with the larger rotor diameter, and also in toward the center of the car to deal with the deeper hat on the Cobra rotor. Dave Dalke aka Super Coupes Unlimited makes a really nice version of the brackets machined out of billet aluminum, and his kit comes with the needed hardware and even centering rings to center Cobra rotors on T-bird hubs (which you won’t use if you already have Cobra hubs). Here is a link to his kit.