The Cobra IRS is an improved and strengthened version of the older MN12 IRS that came in the TBird and Lincoln MarkVIII. It has the same bolt pattern as the Ranger. I have one in my garage if you need measurements.
The MN12 has a different bolt pattern than the Ranger, but you can swap to Cobra hubs/brakes if you want. The Lincoln version got the aluminum carrier as Don noted, and also got aluminum lower control arms if my memory is correct. This guy used the truckirs kit with an MN12:
http://www.therangerstation.com/forums/showthread.php?t=158351
The Explorer that Don mentioned would be Ranger bolt pattern. Haven't seen it done.
The Nissan 240sx would be the same bolt pattern too. Maybe you can find a drifter or import drag racer that's looking for a solid axle for their 240, and work out a swap.
You're going to have to do some fabbing to make any of them work. You can weld on the kit from Truckirs.com. That will let the whole IRS assembly be bolt in, but it sticks out from the frame a fair bit and limits the wheel offset and tire width you can run.
Or, you can do what they did on Trucks, and do some more cutting/welding to make it bolt in, but narrow enough to allow for really wide rear tires.
Pretty sure that any of the IRS units I mentioned will be wider than your stock rear axle, so keep that in mind. Wide wheels with normal Ranger/Mustang offsets will require the body to be modified if you're planning on keeping the wheels inside the wheel wells.