Alot of guys I've talked to recommend just getting a 4th gen rear end unit with the discs. Would be a substantial savings versus buying a whole new one.
The gear swap comprises of a decent afternoon of gutting the whole differential case. You do have to be intricate and detailed when it comes down to getting it dialed in. Most kits come with instruction, but you will need a dial indicator to say the least. And definately posi, was lucky enough to already have, but clutch pack is letting go from 'driving'.