I need somemore advice!

What is the cheapest way to update a 9" Ford rearend to disc brakes with parking brakes?
The guy that sold me the Shell Valley Cobra, says that he thinks the rearend came off of a 1978 Cougar. I do not know if it is a small bearing, a big old style bearing or a big new style bearing. It is kinda of confusing to me!
Thanks in advance for any help!
Killer