If I were you i'd just order the Montero Sport axle from a junkyard, get the one with the locking diff. then you will have disc brakes and an air locker for hundreds of dollars. It's an easy swap, you'll need to drill your pinion flange and clearance the radius for the bolt heads.

There's one in South Bend Indiana for $150 4.63 ratio, you confirm the disc brakes.

Veldman's Auto Parts 1-800-888-3821

1999 Montero SAS'd on Kings and stuff

1998 Montero trying to get a V8 Swapped