Another thing that we Mustang owners must do is strenghten our torque boxes, uppers and lowers.  This is mandatory for drag racers or road racers (unless you're using a torque arm) due to using a drag radial, ET street, or slicks (or if you change your control arms to polyurethane bushings or solid bushings.  The torque boxes often will rip off the car when slicks are run at the track, at a minimum, the sheet metal will distort and fatigue from the continuous abuse of racing and eventually fail.  The best way to solve your torque box blues is to have them fully welded, top and bottom, and to plate the bottom of the lowers.  This is not something that we would recommend having done at a muffler shop, the body filler & paint must be prep'd before welding and the rear end must hang free.  This process has been proven to work on all drag and road racing Mustangs (David Wolfe of Wolfe Racecraft has been doing this process for over 10 years and they haven't had one car come back with damage to the torque boxes) and it worked on my Mustang and I shock my tires really hard on the launch!  The after market replacement boxes are not necessary, getting them fully welded is the best solution.  (If you have already damaged your torque boxes, we can repair them.)