Like Jeff said, you can't interchange the two. But you can take the carrier and ring and pinion from one rear to another. You must keep the ring and pinion together because they are a matched set. You can't just replace the ring gear or the pinion. You don't want to do any of this at home unless you've done it before or know someone who can bail you out when you get stuck (like the mustang works site, lol) Setting the backlash is a tricky thing to do, especially when you tighten the pinion nut too much. There are several sites that have instructions on how to do this.
Just for a piece of mind.....
http://www.thedirtforum.com/differential.htm
Well put, Jeff. You hadn't posted when I began typing mine, lol.