If you decide to swap the rear end to go to a five bolt pattern, or do a front disc brake conversion (very easy), I would suggest using the 5 lug on 5" pattern instead of 5 lug on 4 3/4. I'm in the process of that right now and have found many GM 10 bolt positraction/limited slip differentials that are 62" from wheel mount surface to wheel mount surface, which is what my truck is, but they have all been '5 on 5'. They are all under Chevy Caprice's, Caprice Wagons, Olds Cutlass Supremes, Pontiac Grand Prix's, and other large sedans/coupes. I haven't had any luck at all finding a posi 5 on 4 3/4.
If you want to keep your stock axel and convert you might look at speedwaymotors.com, they have a rear axel conversion to DISC brakes for around $300, not including a new master cylinder.
