Well, I couldn't ever find the video that I was looking for to link here. However, it seems that the 3.0 gets a bunch of bad reviews for it starving for oil from time to time. The sump clogs, or something of that like. Honestly, I've not had the opportunity to investigate it any futher. At the same time though, there are plenty of people who praise their GU with a 3.0 in it. Honestly though, I have seen less negative conversation on the web about the 4.2 than the 3.0. The 2.8 seems to have the complaint that it's just underpowered. Still, have a Trooper/Jackaroo that is running a 2.8 tdi (4jb1-ti), I can imagine the Patrol wouldn't win any races, but still has the torque you would be looking for.
So, as to weather or not you should get the newer, or one of the older... That's a hard decision. IDK. Seems to me, the older ones could have more potential for your future. Importation possibilities, building/modding it to your prefference (for a the same cost as the newer, maybe even less). Where as with the newer one, you'll be getting a new a newer vehicle at a higher cost that's already modded. Still, will you be completely satisfied with all the mods as they are? My experience shows, that that is very unlikely. Almost everybody that I know who has purchased a modded car/rig has started "tweaking it" shortly after buying it, and the eventually end up changing almost everything that was already modded.
Also, something to think about is the following. I'm sure that you've looked into the cost of shipping your RTT, but if it's as expensive to ship to Guatamala as it is to Chile, you may be better off looking at building a sleeping platform in the back with slide out drawers, and just sleeping in the back of the rig. While sleeping you can fold down the back seats and store gear there, plus your roof rack. It'd probably be cheaper and work pretty good. Once again though just a suggestion.
So, trying to clarify a bit more... If the older are in GOOD shape, motor/chassis/mechanically over all/body/ect.. I would probably lean more toward them (personally). Still, I don't think the 2003 would be a bad option either. I just like my rigs to be to my specs. Not those of some other owner, and the 3.0 dialog on the web, would make me a bit hessitant.
Check out this thread and forum though if you can before deciding.
http://www.patrol4x4.com/forum/nissan-patrol-gu-gr-10/3-0l-problems-18293/
Hope it works out either way. Make sure you let us know.