I saw an edition of Extreme 4x4 a while back (
http://www.powerblocktv.com/sites/xtreme/xt_ep.php) in which they swapped for Rockwells and used a front as a rear... They had some rearranging to do, and added a caliper and disc at the pinion for front brakes.
I'm sure you could probably find a reverse-cut Dana 60 pretty cheap.
