Dakar Rally Raid Trucks

[sassgrunt]

RC Channel makes several aftermarket axles to replace Tamiya axles, including 4x4 types. They sell a 'Dakar' setup that includes axles and transmission here: http://www.rcchannel.com.tw/product_...roducts_id=410
Be advised that all of their transmissions are one speed (although they include three different gears that will allow you to decide on what final ratio you want).
As far as trying to make a suspension with more articulation, remember that a Dakar truck does not have the jaw-dropping flexibility that a rock crawler does.
The Tamiya Mercedes delivery truck is a good start if you don't want to build your own rear box, but if you want to build your own, then the Tamiya Scania cab might be worth looking at.
There are also suitable stickers available that will make marking it a lot easier. https://www.ebay.com/p/RC-Dakar-Rock...HPI/1633148620