Quick google search for those not familiar w/ the 93R:
Durning the 1993 model year, Ford released a competition-oriented version of its already unique 1993 Mustang Cobra. The Mustang Cobra with the "R" Competition Package was built and sold as a two-passenger automobile with specialty seating and the 1993 Cobra's "GT-40" powertrain. The race-oriented 1993 R package involves improvements in the cars' structure, chassis, cooling, and braking abilities. Ford's weight-reduction program called for the elimination of the air-conditioning, radio, speakers, rear seats, rear carpeting, filler panels, insulation, padding, seam sealer, and rear safety belts. The factory's weight-reduction program was effected by eliminating nearly 400 pounds from each car and then building in approximately 250 pounds of structure, equipment, and added fluid capacity. The major portion of the weight put back in is attributed to the radiator's increased capacity, the de-gas tank, the oil coolers and their plumbing, the chassis stiffening and bracing, bigger brakes, the extra wheel lugs and nuts, and the use of a full-size spare tire and wheel.
The 1993 Mustang Cobra R-Model was designed and prepared by Ford for customers to race in endurance roadcourse contests. Ford had wanted to put the same recognizable race car models on the track that they sold to the general public for street use. The endurance races initially involved were typically 1, 3, 6, 12, and 24-hour events held by the SCCA and IMSA sanctioning organizations. At the time of its production, the R-Model was designed to be eligible in IMSA's Firehawk series' Grand Sports classes and in the SCCA's World Challenge "A" and "B" categories (for Pro-Racing). The cars were also eligible to compete in the SCCA's Improved Touring (IT) "E" category, the American Sedan class, and in F/Stock Solo I and Solo II and in the S6 division in the Pro Solo autocross classes.
Durning the 1960's, Ford used the letter "R" in select production vehicles' identification numbers (VINs) to indicate that the car was equipped with the maximum-performance version of that model's most potent powerplant. In time, these models were commonly referred to as "R-code cars," "R-cars," and "R-models." The "R" model designation was also applied to Carroll Shelby's competition-prepared version of the 1965 Mustang GT-350 (only 36 GT-350 "R's" were produced and are currently valued at nearly $250,000). Ford also built R-Models in 1995 (250 units) and in 2000 (300 units). The 93 limited-production Cobra R-Models were the last special-edition Fox cars offered by Ford Motor Company and the first "R" model produced by Ford's Special Vehicle Team (SVT). Only 107 R models were built in 1993, thus the 1993 Cobra "R" is the rarest, fastest, most collectible of all 5-liter (5.0) breeds. The 1993 Cobra "R" is one of the rarest factory production models in Mustang history.