Hello there,
The 3L is a pretty good engine from a reliability point of view as long as you dont overheat it.
I managed to crack my head by doing so, but it was purely my own fault. A plugged rad is a very bad thing to ignore.
In naturally aspirated bone stock from, the truck will be pretty slow, but also very near to deserving the term "bulletproof". Tediously so to some, I recommend you test drive it on the highway ahead of time.
A turbo swap from a 2LT is a relatively simple and cost effective upgrade provided to you can do the work yourself. Set up conservatively it is a huge improvement in everyday driveability. But, not certainly not necissary just to get into the woods.
That being said, as a mechanically injected diesel, you will be hard pressed to find a more reliable engine for off road use. Very little to go wrong, as there are minimal electric goodies to fry.
I have a friend with basically the same truck who plugged up his alternator so bad one night it wouldn't charge at all, using his lights killed the battery almost totally, truck stayed running just fine.
A truck like that is, in my opinion, an excellent build platform.
I have a 1990 LN106, ie the same truck as pictured above. I've since added the turbo mentioned, bumpers, sliders, skid, two lockers, dual t-case setup, homebrew snorkle, 4.88s, and 35's, all done a little at a time. I've run mine through a whole lot of sh*t and abuse including a trip down to the rubicon, wheeled craziness all the way from ontario to the foothills of alberta, to the bc interior and its stood up really well. I drove it for months with the head cracked thinking it was just the gasket, still ran like a champ. Truck was and still is my daily driver.
Water over the hood, ridiculous cold, desert heat, all in a days work. How many people could get into their rig, drive it 3000km, wheel like crazy and drive it back without issue?
With a bit of maintenence, that truck will never let you down.
Start slow with a decent set of tires, add a rear locker, and for the sake of insurance a snorkle, and you will be equipped to run any trail your skill level will allow. Mod as your skills progress, and you will end up with a hell of a rig.