Newer mustang GT or base with the factory 17" bullitt style wheels. This spare may be the right diameter to match your tire diameter on the rear. As another poster said earlier in this thread mismatched diameter tires on the rear even if its a spare to limp home can wipe out clutches in a sure grip.
I have a 2007 mustang GT, i can measure the width, and tire diameter and post here if anybody is interested. I am sure it will clear the discs as my GT discs are pretty big, and it has a 5 on 4&1/2" pattern.
Need to check anyways as i need a compact spare for my project car as well.
Matt