Skooter_Built
Observer
I wouldn't swap the axle. There are several places that have Dana 70 rear disc brake conversions.
http://www.ruffstuffspecialties.com/catalog/BoltOn.html
http://www.greatlakeoffroad.com/GLO-Dana-60-and-70-Disc-Conversion-Kit.html
I thought about swapping to rear disc's on VanDOOM as it has the 70 in it, but frankly the drums have more initial stopping power and bite than discs, but discs are much more resistant to water etc.
Kind of a crap shoot really.
Use Cadillac Eldorado rear calipers if you want parking brakes. If your going to convert your current axle to disks, they will work with the brackets with a little work.
http://www.pirate4x4.com/forum/chevy/1081186-14-bolt-disk-brake-conversion-e-brake.html
I personally believe they are useless but just want to pass along my knowledge.