Hello Ahmed - welcome to the forum.
Looking at the pics and reading the specifications you have listed, it sounds very much like the base spec vehicles we were receiving in the mid 90s (from about 1995 on we were getting the 3.5V6.)
Mechanically, it sounds very much like mine. I only have the 12 valve version of the 3.0 - I presume that one is a 24 valve motor?
Offroad, they have a pretty good power to weight ratio (even mine with 109kW), and mine certainly doesn't mind sand - although we don't have dunes like yours.
I've never had cooling trouble with mine - the only time the gauge has moved above normal was when I split a radiator hose. However, I haven't done a lot of hard driving in 45deg heat. I have done some low range soft sand work in temperatures around 40 degrees, and it had no trouble.
Over here, most vehicles of that age received a good LSD, and mine still seems to work pretty well. ARB make an air locker to suit the rear diff, not sure about auto-lockers. ARB also make a front locker which should suit your vehicle (AFAIK it suits all V6 manual Pajeros, and I have no reason to doubt that it suits yours.)
A company here in Australia has designed low range reduction gears to suit two different versions of the Paj transfer case, so there's a good chance that one suits whichever case is in that vehicle. However, I'm not sure if they're routinely available, or only when there's enough demand to produce a batch. I have 2.85 low range gears in mine, and I think they're great.
Replacing the engine fan with an electrical unit shouldn't be a problem. If you have any luck with the search function I think it's been discussed here a few times.
Cheers,
Scott