Nine inch rears aren't hard to find, eights are a little scarcer. No if you want a either that fits a Stang, without narrowing it, now that's a little harder to do.I sold the Versailles rear, but if you want one to narrow, I have a bare 9" from a 68 F100 to sell---cheap.
I bought a complete unit from the Cougar guy in Oregon years ago.
I've also got a bare 9-inch truck housing (actually a Bronco I beleive) sitting in my garage (in the way) it is a big bearing 9 and would need to be narrowed as well. Figured I'd use it on a race car someday...
I've also got a complete center chunk from a 68 Cougar XR7 that can go with it, as well as a pair of 28spline axles that also fit your mustang.