Ah, the plot thickens.... Both interesting trucks. That Tatra is a brute! They still look so dated though and low. The huge engine lump in the cab would be a big negative in my book. The Cummins would be great tho. It's already a crew cab and you are not doing Europe so it ticks more of your boxes than the Mercedes... However, I'd still buy the Merc
as I love the look of them (especially the last of the 4x4/6x6's with the MK/SK cab). If you did go down the Mercedes route, I wouldn't even consider doing anything with those 1222A dual cabs. They are an earlier cab (Google Mercedes NG cab) with an older dashboard. You'd be buying 2 trucks to make what you want. The 1222a would then go up in value as it would now become a 4x4 with a late cab (ideal overland material), and the 2631 would go down in value as it is a later 6x6 with an early crewcab... Most remove the old fire body's as they don't actually have a huge amount of space in them. Your money would be better spent getting a good coachbuilder to modify the 2631AK. Alternatively leave it as a single cab and build your living box with forward facing seating in mind. This saves the crewcab issue/mods, gives you more living space for those times when its just two people and means you can build it how you want. What's the age limit for bringing a truck into the US? Can you bring that 2631AK in? Being a 2631, it will be rated at 26 tonnes and have the later OM441A V6 turbo diesel rated at 310 hp. This is a good engine, and a lot smoother than the earlier OM421 V6 which always sounded like an empty tin with 6 nuts being rattled. Hard decision tho. Have you driven the Tatra? That would be my first suggestion.