You're right, the owner said it was replaced with a 9 inch rear. My mind wasn't thinking right.

 

If it really is a 9 inch you scored its one of the best rear ends ford made,But still try putting a socket on the lowest 3rd member bolt to make sure is one.A site you'll need is http://www.discbrakeswap.com/ he has a kit that comes with spindles and disc brakes that changes the front to a 5 lug too.