Mustang Cobra IRS in an A-body

I have been toying with the idea of trying to make this work...my main problem is trying to figure out how wide I can have a rear end, be rotor to rotor or hub to hub. The stock A-body 8 3/4 is from my measurements almost exactly 57" hub to hub. The cobra suspension is apparently (from what I've been told) is 61" rotor to rotor. I plan on rolling the rear quarter wheel lips and other things, but I just can't seem to be able to picture what would happen should I swap that rear end into the duster. Anyone have any ideas? or heard of a similar case custom job?