I was talking about the differential gears. The transfer cases are specific to the transmissions being used. I have not seen a transfer case gear change in a Gen 3, but that does not mean it is impossible. I know it would be more expensive than beneficial.
I will post this in the forum as well.
You would need to replace both the front and rear differentials to go from 4.3 to 4.9. Otherwise your AWD and 4WD will not work at all. I only did a rear differential change, but I kept the 4.3 ratio. I needed to replace a bad differential and added an LSD in the process.
For the actual swap, you need to locate 4.9 parts from an 01-02 XLS with a 4-speed transmission. This is easiest to confirm by looking for a manual transfer case shifter. LSDs in those models were not standard, so most may not be. The Limited 5-speed models were more common to have LSDs. Some have said it was standard, but I have seen some without.
The rear differential is a pretty easy swap and can be done without jackstands:
Order an entire assembly WITH side output flanges (
http://www.ebay.com/itm/2001-2002-FULL-SIZE-MONTERO-XLS-4X4-REAR-DIFFERENTIAL-/192110778862?fits=Model%3AMontero&hash=item2cbab1d9ee:g:tUgAAOSwB09YM77E&vxp=mtr)
Put the parking brake on and place the transmission in N. This will lock the side axles but let you rotate the driveshaft once unbolted.
Chock the wheels as well. Be very careful on a slope
Remove the rear breather hose <<<<There is a plastic fitting in the housing that may break if the hose stays connected - Ask me how I know
Use a paint pen to mark the driveshaft and differential input flange. This is to mark it for balance purposes in case you want to switch back. Paint pens last much longer than Sharpies.
Make the same marks for the two rear axles.
The rear axles are attached to the output flanges with 6 bolts each.
The driveshaft has 6 bolts as well.
***This part helps to have another person***
Use a jack to support the differential. Unbolt the 2 bolts at the front and 2 bolts at the rear.
Lower the assembly and take it out of the car.
Move the large rubber/steel isolator from old diff to the new one.
Install in reverse order. Check fluid levels and use Mitsubishi LSD oil if you purchased a Hybrid LSD one.
I have not done a front swap, but it can be done by changing the entire front section (
http://www.ebay.com/itm/01-02-MITSUBISHI-MONTERO-FRONT-DIFFERENTIAL-PIG-CHUNK-AUTOMATIC-XLS-/391546949271?hash=item5b2a044e97:g:B1EAAOSw3KFWcJ-v&vxp=mtr). There is also information out there about it.
Use the FSM to check for anything that I might have missed, but it has good diagrams of everything.
***A word on the Montero/Pajero LSD***
Mitsubishi uses a Hybrid LSD in the 01-02 Monteros. This unit combines a Torsen/gear LSD with a clutch to provide preload in free-wheel situations. The gears are much more durable, but Torsen units cannot function with a wheel in the air because the output torque becomes 0 on both sides even though speed is different. To compensate for this situation, Mitubishi employs a small clutch pack that heats up and engages when the speed difference is high. This provides enough torque to get the worm gears interlocked. This system needs Mitsubishi LSD oil to allow proper function of the clutch. The LSD also works with the 03+ traction control without causing problems.
