bid axle Montero(Pajero) with 4.9 was only available overseas on 2.8TD version.
Montero Sport 2000+ 3.5L versions came with 4.9 in big axle but didn't have selectable locker. They only had LSD (all of Ltd and some of XLSs) albeit very good (possibly best?) one.
I you want to install locker into that you would need 3rd member and axles out of 98-99 Monty. They either swap R&P or modify existing house to accept airline and switch, and swap lockable differential only.

Alternatively you can get M/S axle and install new ARB locker which are just coming out.

92 SR, 285/75R16 Yoko MT ARB locker GAST compressor AirLift 1000 MM10500 Snorkel custom rear bumper
02 Montero LS died protecting the master
08 PowerWagon (stock!)