The 99-04 Cobra IRS was a by design, a compromised set up as they were designed to fit within the set confines of the existing Mustang platform. I knew guys who autocrossed them and the geometry was not ideal. A well set up solid axle Mustang does much better than they do with the 99-04 irs. About the only thing they do better is ride quality.
I'm not familiar with the Mustang set up. But the idea of adapting a C2/C3 design into something that looks & functions as if it was on the drawling board in the early-mid '70's is what I have thought of over the years. Working it into a bolt in cradle that doesn't clutter up the what could be usable space is one thing I would try. Then trying to figure out a mono leaf, coil overs or just regular coils/shocks. Besides using the control arm mounts use the coil pockets to be used for additional mounting points. One issue I can't figure out what kind a exhaust clearance would there be. Wish I had the drawling skills to try to draw it up.
