These would be a definite improvement as they are tubular design. Stock 1998 Mustang GT and Cobra used a stamped design. Tubular control arms offer improved handling and launch characteristics. They also come with polyurethane bushings.
Warranty Note - The use of any grease other than urethane bushing grease (most commonly seen in small packets labeled by Prothane) will void the warranty of your control arm bushings. Bushings must be fully coated in the proper lubricant before installing the control arms.