The stock SN95 rear suspension is garbage, plain and simple. The front is not great, but not nearly as bad as the rear. Right after I bought my '95 R I took it to Laguna Seca for a weekend of fun with the NorCal Shelby Club. On Monday when I put the car up on jack stands to do my creeper tour and got underneath the car I noticed that the inside of the rear tires had been rubbing against the tailpipes on BOTH SIDES! There's 3 inches of clearance on each side, so that means the rear axle was moving back and forth laterally AT LEAST SIX INCHES! Holy cow. This is factory race Mustang suspension? I tried some polyurethane bushings, then aftermarket arms, but they all seemed to make the car oversteer. Nothing seemed to work.
I decided to call Bruce Griggs (Griggs Racing). Bruce told me that the rear suspension of my '95 Cobra R dates back to the 1977 Ford Fairmont. OUCH! He also said "we have a solution for that". I ended up bringing the car to his shop at Sears Point and left it there for 8 months (and $$$$$) where it received their full World Challenge frame and suspension setup (not SLA).
My experience is that it is truly difficult to improve the stock rear setup without causing undesired effects. When these Cobra Rs were raced they left the control arms and bushings stock and only changed sway bars and shocks.
If you look closely at the rear control arms you'll notice that the upper and lower arms operate on different planes. They all connect to the same axle, but pivot in different directions. What this means is that the arms tend to BIND when the suspension moves. This is why the rear control arms are designed so flimsy and use soft rubber bushings. If you put stiffer arms and stiffer bushings you increase the binding. It is my understanding this is what causes the oversteer. This is what the Griggs and MM suspension cures.
I know. I sound like a shill for Griggs. It's not that. I'm just a highly satisfied customer. I can now enjoy a truly world class race quality suspension so I can drive 100 MPH through turns leaving four thick black stripes as I drift in a controlled sideways slide to the edge of the track putting 600HP to the ground (with my Torsen T2-R Racemaster differential fighting for every last bit of traction). This is what I built my car to do, not drag race. What I need now is more tire on the ground, but for that I need new wheels... Off to a new thread!