Two main types of Discovery, the 1994-98 model and the 1999-2004ish model. So "Late 90s" could be either. I have owned both, though not the NAS version. Kept the last one (2002 D2) until last year and had very few problems with it.
Later Discovery II vehicles are/were more reliable but the earlier vehicles are more suitable for tinkering - there are not a lot of electronics in them. You can buy diagnostic kit for all of them though, at least in the UK. Need to check if the diagnostics cover the NAS versions.
NAS vehicles will all be LHD V8 and auto gearbox. The earlier vehicles are mainly nuts and bolts engineering underneath, later ones have more electronics but nothing much by comparison to current vehicles. Corrosion of the bodywork can be fatal so have a good look around but if it drives OK, and looks OK, then it probably is. The good thing about them is that with a new set of suspension bushes, springs and dampers, you can end up with something that drives almost like a new one. I don't know how easy it is to get parts over there but UK exporters will send stuff overseas (Bearmach etc) - the only snag might be any parts specific to the NAS vehicles.
Join one of the Land Rover forums for more advice, though many of the forums are Europe based so advice specific to NAS vehicles is probably going to be limited.
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