Others know more about this than I do, but it's likely that the cabin dimensions you want will affect the truck you'll want to choose. I don't know the wheelbase of the 2450 for sale, but some 2450s will accomodate a longer cabin than a U500. And, similarly, some 2450s will be able to mount the cabin a bit lower than on a U500, which requires the cabin floor to be pretty high in the air.
The U500 will be the nicer ride; the basic design of the truck is about two decades newer and it's more way more sophisticated and with a nicer engine and transmission. Some argue that the US-legal U500 is less desirable because it's from the MBz Mog "implement carrier" line rather than the "off-road" line (those, as Charlie mentioned, were the U3000, 4000 and 5000; never legal here). And others argue that the U500 is too complicated and computerized to work for third world use.
I personally don't find either agrument compelling. If reducing complexity is critical to your journey, then you'd want the 416 series, which is the last Mog comprehensibly fixable by the village mechanic. And where the heck you going to go that's too rugged for the U500? Either a U500 or a 2450 is going to yield a camper that's way too big to be doing technical stuff anyway. To me, the most important issue is how the cabin you want will fit on the chassis. If it's six of one, half a dozen of the other, a U500 seems the better choice, if you're not adding any significant value for the U2450's cabin.
charlieaarons said:
If a 2450 registered legally in the US is for sale, consider buying it if the price is right . . .
If you buy any Mog from anywhere, oh do make sure that you can get the truck registered in your state. Nothing makes a worse paperweight than an undriveable Mog, and there have been a few.