[Three Peaks]

Yes, the T-bird has a wider track width.

Installing one in a Cobra is a completely different ballgame than trying to retrofit one into a Mustang.
It can be done, but you'll have to add all the mounting brackets, a subframe, and shock mounts and suspension pick ups to your existing frame. Then, you would need to have the axles shortened and the hubs drilled to the Mustang bolt pattern.

If you can find a Cobra unit, it should practically be a bolt in.

Cobras that are designed for the T-bird IRS (such as FFR) have all these points in place so it is a bolt in proposition.

Check with some of the Mustang forums to see how difficult it would be to do the retrofit. I'm just not that familiar with Mustangs to be sure.