The Mercedes diesel engines are dang near bulletproof. Good fuel mileage, too. People commonly get 300,000 miles on them and they still run well. Some people get into the 500,000 mile range with them as well.
In researching engine swaps for my '90 Ranger, the OM617 from an 83-85 Mercedes 300 looked like a good candidate. The engine was rated at about 125hp from the factor but could be bumped to 145 just by turning the injector pump up. Any more power than that requires modifying the injector pump. Plus, the engine can still rev to about 5,000 RPM, unlike many diesels which like to stay around 3,000 RPM.
That looks like a fairly decent find, all the hard work is done for you. Just need to make it run! I thought I remembered seeing the white gen3 Ranger with an OM617 somewhere on TRS...