'49chev,
I'm currently converting my '59 3800 to a 4x4. I bought a Dana 60 front axle from a wrecker (sorry, automotive recycler) that has the exact spring spacing as my '59, had some u-bolts made up and it bolted right up. I'm converting over to power steering, so that's no big deal.
Find a 'divorce mount' NP-205 transfer case from an early '70's International pickup, that way you won't have to do anything to your original driveline, just a short driveshaft from the tranny to the transfer case, one to the front axle and a shorter one to the rear axle.
Check out the progress here:
http://community.webshots.com/user/Lane9999Lane