Unimog Club UK

As everyone has said before, the u1300 is ideal for overland. Most countries have had some involvement with unimogs, be it the goverment, multinationals (eg oil exploration) or NGO humanitarian organisations so there is likely to be a service and supply route for parts set up.
Another point is that many "complicated" mogs are ag spec so have hydraulics and PTOs etc, an ex military u1300 would have non of that to worry about.
If you are doing a lot of road miles choose your tyres carefully as they make a big difference.