Thanks for having the thread title edited. I had our computer guy look over the e-mail server for your 10/30 e-mail. He wasn't able to find it. I do have the e-mail that you posted above and sent me on 12/6. I have been out of work since about 12/3. The thread below has some details about this in posts #26 and #34.
I ended up in the hospital for about a week as a result and have only been able to do a very small amount of work for the last week. To complicate matters, my wife is now sick with what I had, so I've been caring for her for the last four or five days. I know that it is frustrating that you weren't able to get a response in a reasonable time, but in this case, there was just no way for me to deal with your e-mail given the situation I was in.
My e-mail has my direct phone number in the signature in it. You can call this at any time. If I can, I'll answer it. If I don't return your call within eight hours or so, that normally means that I can't. In that case, just call the MM office number and speak with someone there. If I am not available, they will be able to tell you that.
I think that your car has been lowered much more than you realize.
From the factory, there is a mass damper that is bolted to the bottom of the ears on the differential. This damper has a metal bracket that goes over the top of the ears. This bracket serves two purposes. One is to be a nutplate for the nuts. The other is to be a surface for the pinion snubber to bottom on. See the links of photos below of the bracket and damper
The surface of this bracket for the snubber to contact is about 1.5" above the top of the differential casting. Your car is missing this bracket and mass damper. Given that the snubber is 2" from the top of the casting, this puts the car only 0.5" from where it would be contacting the metal bracket and that is with the shorter aftermarket snubber. With a stock snubber, it would be resting against the bracket at ride height.
Notice how far the front wheels are pulled rearwards in the front wheel wells? This is due to the amount that the car is lowered. At stock ride height, the wheels are centered fore/aft. As the car is lowered, the wheel moves rearwards in the opening due to the angle of the FCA pivots in the plan (top) view.
Before doing anything, I would do what is called a metal to metal analysis. This means to remove all bumpstops from the suspension and springs. Then slowly cycle the suspension from ride height to full bump with a jack. There are four places where you will have metal to metal contact on your car.
1) Axle tubes to frame rails.
2) Shock body bottoming inside upper spring perch.
3) Driveshaft to bottom of parking brake cable brackets below parking brake handle.
4) Driveshaft to transmission tunnel just in front of rear u-joint.
#1 is an absolute limit that can not be changed.
#2 might be a limitation, but can be improved upon with the racing shock mounts or other fabrication.
#3 is a common problem and can only be fixed somewhat by grinding the bracket. If the bracket hits the driveshaft very much, the driveshaft will get a groove machined in it and will be ruined.
#4 requires extensive hammering of the tunnel.
Cycle the rear suspension very slowly. Once you run into the bump limitation on your car, stop. Precisely record how much further the suspension could move for each of the other three possible travel limitations. This is important to do. If you fix the limitation, but find that the next limit is only 1/8" further, then there may have been no point.
It is possible to shorten the bumpstop, but don't do so until after we have data for all of the above.
The racing upper shock mount will increase bump travel and can be modified to add even more bump travel, but you don't want to install it until after you have looked at the above limitations.
In the front, you definitely want to use Koni struts for a Fox Mustang. They will give the car 1.02" more bump travel in front. ..The 29mm swaybar on the front of the car will work fine.
With the 325lbs/in front springs, I would keep the 200lbs/in rear springs.
With a 350lbs/in front spring, I would also keep the 200lbs/in rear spring. This combination will actually have slightly better ride quality.
I would use an MMRSB-5.1 rear swaybar (7/8" x 0.188").