Although the bolt pattern is the same, the Mustang wheels have more offset than Trac/Explorer/Ranger wheels meaning that the tire/wheel combo will be tucked closer to the body than is usually desired. Also some Mustang wheels run into clearance issues with the front hub. Both problems can be overcome with spacers, but that's a whole new can of worms.
I saw a white Ranger 4x4 with white Cobra R rims once, with the tires so close to the body it looked kinda silly IMO. :wacko: