I'd at least get a quote for rebuilding your center section with 3.55 gears and suregrip locally. Have you called Sutton Engineering at 817 E Lambert Rd, La Habra, CA 90631
(562) 266-0044 ? He's not too far from you.
Another option would be for Sutton Eng to redrill your existing axles and drums for 4.5" pattern for under $200. I did this 22 years ago and it was like $90.
Bummer is you can get a Dana rear without brakes for $2150. And you could sell you existing rear for $500-$600.