5.29's are in the for sale section right now, if you don't buy those you will have a tough time finding more later at least at that price.

you can use a super select transfer case from a gen 2 with a 12v 3.0 but you will need custom driveshafts. and that t-case still takes Marks 2.85 gear set. In order to run the big t-case and 3.15's you'll need the gen 2 tailhousing to match the transfer case. you'd be better off swapping in a rubicon rock trac t-case at that point as they bolt up and are 4:1. You'd still need custom driveshafts and speedo like you will with the gen 2 cases. What are your plans for the truck? how are you going to use it?