Yesterday, I did some general measuring of both the Chevy and the Mercedes engines. They are VERY similar in size, I don't see any issue there at all.
As best I could see with the engines still in the way, the motor mounts are similar styles and locations.
While digging through Craigslist, I found a person not too far away who had a large selection of old automotive books for sale, mostly for European cars.
I was able to pick up a couple of books for $5 each. One specific to Mercedes diesels, one for all Mercedes of that era, a really nice 2000-page professional import repair manual, and the Idiots Guide to Motorcycles (for my electric motorcycle project.)
I also found a 1995 Chevy S10 on Craigslist. Same year, model, size, and style as my truck, for $500. I called the same day the listing was posted, and asked the guy if I could come see it (only about 10 miles away!) He said to stop by the next day. When I called the next day, it went straight to his voice mail saying the truck was already sold.
Now that I have some Mercedes diesel manuals, I can really start reading through them and start figuring out a few things. For example, the driveshaft is multi-part, with some strange connections on it. Much easier to look at a diagram in a book, than to have to jack up the car in the driveway in the cold.
One of the books also lists all the different transmissions used in these cars.
The 240D (the one I have, with the 4-cylinder engine) was the only one available with a manual transmission. The illustration of the manual transmission is crazy looking. It has 3 arms on there for shifting. My metro just has one rod!
The 300D, a very popular 5 cylinder diesel used the same automatic transmission. I did find a machine shop in California who are building adapters for the engine from the 300D to go onto GM automatic transmissions. That means their kit SHOULD also fit the 4 cylinder engine! Their kits aren't out for production quite yet, and cost more money than I would really want to spend.