disc brake conversion need help

Do you want to spend money and just bolt something up? Or are you short on cash and need to spend as little as possible?

Baer and Wilwood have kits

Ford Motorsports has a rear disc kit that's made of '99 Explorer parts. It fits on a big bearing 9 inch rear.

On the low budget end, this site has junkyard sources and directions on how-to for a spindle upgrade, and rebuilt/new parts are cheap at any local parts store.
http://www.mustangsteve.com/granadadiscs.html

Some people also do junkyard rear discs from a Versailles or Granada.

http://forums.stangnet.com/showthread.php?t=502531&highlight=pbr+calipers
That thread has some Granada disc upgrade tips. If you have fabrication skills, or you could pay someone to make the brackets.

Do a search on this forum and you'll find a ton of threads discussing this.

Good luck