If you used an 8.8" out of a mustang you'll find you won't have much room at all for wider tires which WILL cause traction issues. Unless you narrow the rear and tub the fenders. Another note about wheel diameter, I purchased 17" diameter Hallibrand Cobra III wheels in order to clear my 12" disc brake calipers. This leaves virtually no room for the front tires in the wheel well. I have bone stock 1978 Mustang II upper and lower control arms and spindles and have Carrera Coil over adjustable shocks set to their tallest setting and the car is still so low that I have to hit some approach's sideways so as not to drag the
oil pan/Scattershield, or drive the tires into the fenders, my driveway being one of them. So... having said that, a smaller diameter wheel will free up some wheel well but will also ultimately lower the car some as well. One thing that helped was when I mounted the body I put a 1" think piece of rubber at the forward cross bar at the corners where the body lays on it.