If I wanted a Toyota diesel, I would have just bought a Toyota, but I didn't want that.
The reason for the merc is that the engine I chose (the OM606) is the most sophisticated non-computer controlled diesel possible - actually it came from the factory with a computer, but by using the injection pump from the earlier OM603 it can be made fully mechanical. This is a boon for repairs, simplicity, and the ability to burn basically anything like kerosene. It also means it's powerful and efficient, and mileage was my number 1 goal.
Also, that Merc engine happens to come from the factory in many cars with exactly the same gearbox as in my Jeep (the NSG370), so things made sense there. Jeep have also used Merc diesels in the past (not in the Wrangler), so that made sense too.
It was an ambitious plan, and I'm glad that I tried, even though it didn't work out in the end.
That aside, I'm in west Africa now, having the time of my life :)