This car was all about taking advantage of NHRA weight breaks. As they stood early in 1974, cars with a wheelbase over 105 inches had to carry 6.45 lb/ci where as cars under 105 wheelbase had to carry 6.85 lbs/ci. In Pro Stock where favorable weight savings are measured in ounces, weight breaks allowed the new Mustang to weigh over 100 pounds less than the Mustang II. Don once again called on Don Hardy to build his new car. As opposed to being built around a body in white, this car would be assembled using separate body panels. Debuting at the 1974 NHRA Grandnationals in August, the best showing for the Mustang came in 1975 as Don won the 7th annual Popular Hot Rodding meet. Changing rules made the car less desirable and a new Mustang II was built. Don had only 35 runs on the Mustang, seven national events in total before parting with it.