A Dana 60 from Ford vans, seems to be a popular option. I don't recall the years, but there is an early Ford Dana 60 that is pretty much a direct bolt on also. Of course, the 14 bolt dually rearend is quite popular also. The benefit of the Dana 60's or the 14 bolt is that you get way more gearing options. The 14 bolt can be found from a 5.14 gearset all the way up to 3.21. The Dana 60, pretty much the same.
Going with a 4x4 front axle would be cool, but what a can of worms it opens up. If your sole goal is disc brakes, why not make a kit yourself. Myself, along a number of other members are working on and a few are even using disc brake setups we've made on out own.
I've came up with a template using GM van calipers and rotors up front and I'm working on adapting late model discs to an early 14 bolt axle. In your situation, it may be just as easy to find a late model axle with disc brakes on it.
I haven't updated in awhile, but here are my pics.
www.photobucket.com/whitedog76pics
