Well even the weakest of Montero Axles are stronger than most other 4x4's axles. PA_JERO ran welded diffs on road and rock crawled 35" tires with crawler gears and didn't actually start breaking front axles until we made the front flex way beyond it's factory geometry. If you leave the IFS stock (T bar crank is fine) you won't have breakage issues even in the harshest service. Way back before anyone had done Gen 2 IFS swaps we went crazy with Gen 2 UCAs with a balljoint flip <img src="/forums/images/graemlins/scared.gif" alt="" />
Yeah the flex was crazy but the tierods broke like they were made of glass, so in short you'll be fine just ask here before you go modifying and we'll keep you on the right track.

As for locker availability you can buy a Montero Sport rear axle with an air locker and possibly disc brakes for a couple hundred bucks and it's almost a bolt in swap. Those axles come in two flavors 9" 28 spline and 9.5" 31 spline. the next most easiest thing is buying those same axles from a Montero SR except they will require you to cut off the supension brackets and weld on spring perches but these axles are easier to find and all of them have disc brakes.

In the front you can swap in the Starion LSD or the V6 Montero front axle giving you options of the bigger Starion LSD, the cheapie guy Aussie locker or the Awesome ARB air locker.

One more thing get 35's <img src="/forums/images/graemlins/kewl.gif" alt="" />