There are a few problems that still need to be addressed with the big block in the W200. One of my buddies put a 12 valve cummins in his m37 off road rig and another buddy just bought a 12 valve parts truck and is going to put the diesel in his '70 W300. I have always wanted to put a diesel in one of our old Power Wagons as well. With the '94-'98 12 valve cummins, you can easily add more hp and torque with some simple modification (fuel plate, injection pump, injectors, etc)and it is a simple engine with little electrical/computer work. Plus I will be looking at towing a few heavy trailers in the future. With the right running gear and engine I will be able to do so. These motors get fairly good gas mileage and are fuel injected which is nice on hills. It is just always something I have wanted to do and seeing some of my buddies with their diesels only makes me want to build one myself.
I just put a '70 340 in my daily driver and have dealt with many gas engines and would really like to try a diesel for once.
Just some of my thoughts.
Hope your build goes well.

Rob

Mountain Springs Power Wagon Service, Paso Robles, CA

1962 W100-340-LU2 winch
1964 W200-340-LU2 winch
1964 W300-318-LU2 winch
1965 W200 Crew Cab- Cummins Diesel