Just got a 1976 300D sedan... for the price of a putting a new battery in it. Not bad...
It runs good -- engine is a rebuilt engine I believe. Non turbo. Doesn't really like starting below 50F or so, but it will start. Transmission.... I have to manually shift it between 1st and 2nd and drive to get decent performance --but I do that on brand new automatic transmission too, so maybe it's not anything wrong with it. It looks like there is some good info on here on adjusting it though.
It has a vegetable oil system already...put in a few years ago by a Colorado school of mines class. I need to figure out the controls.. it's got some thing that senses the temperature and won't let you switch till after it's hot enough, and also runs it for a few minutes after you switch back to purge the oil from the lines before shutting the engine off. I've heard it running on veggie oil back when they did it, and it sounds like a gas engine while idling... no diesel clatter.
I also have another project with a mercedes diesel engine... a 1967 landrover 109 that's getting a 1985 5 cylinder turbodiesel. I have the extra transmission from that engine, that could go in this car if it's transmission really is bad, maybe? If the '85 had the same auto transmission as the '76