Good luck finding an 8.1L burb. They didn't make very many 2500 burbs, and even less with the 8.1L. Add Quadrasteer and it's a total Unicorn...
Locking diff is not hard to add if you want it. Factory G80's are on ebay as rebuilt units for reasonable prices, and any axle shop should be able to make short work of installing one since they will not have to mess with pinion bearings or depth at all, only adjusting/shimming the diff for pattern and preload. (10.5" axle has adjusters both sides, so it's EASY, 9.5" axle has one adjuster and one shim pack, so a little more involved, but usually swapping the shims over from the removed diff is all that's needed...)