I found a local fabricator that has been a great help. The IRS support cage, QA-1 coil over shocks, upper and lower control arms are all fabricated and installed. The 8.8" Torsen differential to be installed soon.

This is a copied post from Stangnet for a S550 IRS cradle. The company is Techno Engines out of Moscow, Russia. 

Hi! We have developed a new irs for the mustang. It is based on s550 components. improved geometry with adjustable toe link. It will be great to work on the track and comfortable on the road. For installation will require a modification of the body, similar to the installation heids IRS. We use energysuspension bushing for easy replacement if necessary. The subframe is assembled from seamless pipes by tig welding. Everything is modeled in the CAD and FEA analyzed to achieve maximum strength with minimum weight. A lot of work has been done and this allows us to get better controllability than when using other solutions. We have just started production and I am looking for people who will be interested in our IRS. We can complete the system for any wheel diameter and used coilovers. If you are interested in this, you can ask me your questions and I will provide you with additional information.  
This was posted on the Stangnet Forum. These folks are located in Moscow, Russia and say they can build you the frame for $5000 and a month fab time. They are involved in the Russian Restomod activities.They can be contacted at  technoengines@gmail.com. Their company name is TechnoEngines. I like the look of their product, but I am not crazy about doing business with Russia.
 

Just started the disassembly phase. I have the interior gutted and now need to pull the engine, trans and wiring harnesses. The follow up step is to take it up to Grave Robbers in Cumming , GA for a structural assessment/repairs. I am looking to do a Coyote install with the Tremec 6 speed trans. I am looking at Mustangs to Fear for the front suspension. My hold up is contacting them on questions about the front spindles and brake fitment. I want to put the 14" Brembo package from FRPP and utilize the Ford hubs. I am investigating installing ABS and want to utilize the Ford hubs and tone rings. 
I want to utilize the Super 8.8" rear end with the Torsen diff. The '15 Mustang rear knuckles look to be a good  starting point with the diff to build the IRS (the GT rear brakes would be a bolt in). Need a design or source for the center section mount to the body, with that the geometry of the upper and lower control arms and toe links fall into place. My concern is the half shaft lengths. The '15 "stang has a wider track than the '65 and I don't know the proper way to shorten the shafts to fit (cut & weld?). 
I retired last March and am now getting into the knuckle busting phase.