I HAVE a mustang on 20s. I would take the advice of the one that OWNS one on twenties, before one that 'knows' mustangs.//content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif
You should not have much travel in the car with acceptable shocks in the rear, and struts/springs in the front, so you should not have any problems due to people being in the back (who rides in the back seat of a mustang, anyways?!)
Hell, I have cheap shocks strapped to the back, cheaper struts up front, and all the way down... (no airbag support...) I don't have enough travel in suspension alone to accomodate the wheel going into the fender to rub.