Holy Bumpers Batman!

Maybe it's just the perspective in that photo but your front bumper looks absolutely massive!

Welcome to the Wire!

Changing the axle gears to 4.90s will give you back a little bit of the gear advantage that you lost with the larger diameter tires - they're available new from Mitsu or you can find used ones in Montero Sports (Nativas in Puerto Rico, although I'm not sure if they came with the same equipment there as in the 50 states).

If you don't have a rear locker, the factory air locking rear axle that came in the Montero SRs is an easy transplant - you'll need the factory air compressor and controller of the donor vehicle also. There is an ARB front air locker available, as well as an "Aussie Locker" passive locking front differential.

You'll need to do more research to verify which axles you have currently, since the PR market Monteros weren't exactly the same as the ones we got here in the upper 50.