Gen 2.5 Locker
I would look to purchase the nicest gen 2.5 you can find. I'd say the locker should be a distant secondary consideration. I own 2 of them and could not find these with a locker here in GA. If you find one with a locker make sure the thing works and has not been sheared to bits by PO engaging the thing with a spinning wheel. You will also soon want to install bigger tires and that involves changing the gear ratio so driving dynamics are not negatively affected. That is an important consideration. A locker with your stock 29's is what it is. Very nice, but most want more. A slugged down vehicle with 33's and stock gearing is not great. So, I say there are two options:
Option 1. Gen 2 SR rear end. Those had a 4.67 and an air locker. If you swap the entire axle the ABS will be messed up. The tone ring is different. The way to do it is to R&R the third member into your existing housing. You will need a shorter driver side axle shaft. The Monty locker third member (gen 2 and gen 2.5) is a bit wider on that side. You can install a left axle shaft from a gen 2.5 with a locker or cut down the existing non locker shaft and extend the splines. I had a respected driveline shop tell me the existing unit can be cut down and splines extended, but caution I have not actually done it. Front side is a R&R job with the entire assembly. Kind of a big job, but not rocket science.
Option 2 is to purchase a third member and front differential assembly from a Montero Sport. Something like years 2000 to 2003, 4x4, with the 3.5 liter. Check these facts they are out on the web, and this site even. I may not have the years right, but has to be 4x4 with the 3.5L. Those have 4.9 gearing. Then you install an ARB RD154 locker into that third member assembly. The Sport third member fits the existing axles. Front end is a big remove and replace job. Then you can run 33's and still be under geared, or run 35's and be about right. I acquired the parts from a junk yard for something like $350, but the yard pulled them for me, which was huge. The ARB locker, compressor and accessories will set you back $1,300. I am in the middle of doing this job myself. If I had to do it again I might have used my Co2 bottle to power the locker and saved a few bucks on the compressor. Montero Sport does not have the servos in the front so the front end always spins. Consider locking hubs.
Good luck
