Lots of Unimogs came with gas engines, such as the Swiss army ones, much cheaper to buy than a diesel one and easier to find. A conversion sounds like a likely project. I'm not sure what engine the 406 diesel is but it is likely more of a truck engine than what I'm considering, ... or I might find a nice diesel one at a reasonable price (doubtful).

70mph is about top-speed with the high-speed gearset on the diesels, would depend also on the engine's max. RPM.

- Jeff
190DT and projects