Rearend Identification

If you are sure you have an 8.8, and it's in a Mustang, it's most likely an Mustang axle, Lincoln or late Tbird Turbo Coupe. If it has quad shock brackets, its most likely a Mustang.

Beyond that...

If it has Ranger axles, then it most likely has a 28 spline differential. The easiest way to identify the rest is to pull the cover and count teeth and see if it is a traction lock. You can try the jack it up and turn the wheels quick check, to see if it has traction lok, and count turns to find the ratio, but its more positive to just look. If it is a bit wider, it may have been the Lincoln or T bird.

I am not a rear disk guy so I can't say much about the brakes.

Or perhaps you're lucky enough to find the tag on one of the cover bolts...
That would go a long way to determining what you've got.