That's an LS which means it does not have the rear locking differential but that's only necessary if you use it for complex/technical trail runs. For basic camping off of a fire road, it should be quite capable without it. That said, the Montero is a very capable and especially underrated 4x4 (probably due to the Mitsu reputation of building the Japanese Zero during WWII).
1) The automatic transmission in most of them is pretty much bullet proof and you rarely hear of them having to be rebuilt. Have the tranny fluid flushed and the filter screen cleaned (does not need to be replaced unless it's damaged).
2) Check that the 4x4 system engages easily. Many owners rarely engage them and the system (CAD system) may need to be cycled several times before it engages.
3) Check for black/blue/gray smoke after a cold start-up and after a short idle (5 min?). It's an indication of failing valve guide seals (not the valves). May also mean you can fail your state vehicle inspection. It can in California anyways. Plus the oil will eventually clog the catalytic converter making it fail sooner.
4) With 170K the front leather seats will likely be shot especially the driver's seat unless he had the leather replaced.
5) Shocks may be shot as well. If they are, simply replace with KYB gas adjust or edelbrock shocks. Avoid the crappy monroe/rancho 5000 shocks as they are not very reliable.
6) Of course check when the timing belt was last done. Should be done every 60K IIRC which means it will be time to do it on your motor. Not an easy job since the front of the motor will need to come off (pulleys, tensioners, ac compressor, alternator, etc.). When it's done, they should also replace pulley (or pulley bearings) as well as the tensioner and also the water pump.
I'm sure there are other things I cant think of right now but those are the basics.
