I'm assuming you are looking for MB500732 and MB500733. I believe the axle would need removed to get the backing plate off. This may keep a lot of places like car-part.com from having them available. Does your LS have a LSD rear diff? If not, it might be an opportunity to find an entire rear end with a LSD. There are some specialty wrecking yards like M&S Recycling http://www.msrecycling.com that have Montero parts. On Facebook there is a Montero Parts Exchange group.

Mitsu # 6 - 98 6G72 Montero Sport, Locking Rear Diff, Aisin Manual Hubs, 31x10.5

Mitsu # 7 - 02 6G74 Montero Limited