The fuel system modifications required to support the OM617 diesel are quite minor. The tank and hard lines are all adequate for use with diesel. To drain the tank, I just hot wired the fuel pump and hooked a length of PVC tubing from the supply line in the engine compartment to a jug. This pumped out all but a couple of cups of fuel. 

Fuel Delivery System

The OM617 uses a lift pump, so the fuel pump and associated parts from the 380 all need to be removed. A couple of nuts and the entire system of pump, filter and accumulator all drop out nicely, after removing the flex lines.

One very important difference between the gas and diesel fuel systems is the fuel strainer.The appear identical in terms of the size, constriction and connector, but the screen size is completely different. The diesel strainer is on the left and tha gas strainer is on the right. Without swapping out the strainer, there is a very high likelihood that the kind of foreign material that develops in diesel tanks would clog the strainer and strand you at a most inopportune time.

Unfortunately there is a high likelihood that you will not be able to get the strainer out without pulling the tank. The tank and strainer are different metals and corrosion often occurs that makes it all but impossible to get the strainer out. I had to pull the tank in order to swap the strainer. It's not a big job, but it is time consuming and awkward.

The entire collection of pump, accumulator and filter is replaced with a simple fuel line. Just cut the existing line off the 300D to get to the bare fitting that screws into the strainer. Do the same for the other end and connect the other end of the hose to the supply line.

It should look something like this when done.

When I put the tank back in I made some modifications. I took the vapor tank off, as it is completely unneeded on a diesel. The center connection on the tank I made a vent by running a tube well above the top level of the tank (see tank center below) I also capped off the vents on either end by looping a line between the two connections and clamping them.

In the engine compartment it is a very simple matter to cut the rubber hose off the ends of both fuel lines (delivery and return) just like with the tank connections, and replace them with 5/16" fuel line with the supply going to the clear fuel filter on the IP and the return line coming back from the fuel filter. 

Don't forget to drill out the restrictor plate in the tank filler to allow diesel nozzles to be able to fill the tank. It's just plastic so if you get a few flakes into the tank it's no big deal. Note: I thought I might have to cut out the plate that is left in the filler, but it turns out the 300D has exactly the same setup.

Replace all the filters and you should be good to go.