PirateMcGee
Expedition Leader
I think the Gen 2 and Montero Sport rear differentials are the same so it is likely that there are ones with lockers. There were also more available gear ratios for the solid axles than the Gen 3 IRS. Gen 3 are always 4.90 with a 4-speed and 4.3 with a 5-speed unless someone made a swap. The Australian groups also have a lot of information for these vehicles.
Unfortunately the Montero SR locker doesn't directly swap into the Montero Sport. Something about one of the axle shafts. However ARB works although the hybrid LSD is good enough for most stuff.