I have not yet done this swap yet but it's high on my list after get-truck-driveable, and my understanding is that it bolts pretty much straight in.
Two caveats:
You should get one from an AWD Sport, so that it doesn't have the disconnect because the disconnect won't fit a Montero
You should invest in a set of manual hubs so when you're rolling 2wd you aren't always spinning your whole front driveshaft and the bottom half of the transfer case.