Ok, making some progress.
We chose to first remove the OM606. The job was pretty straightforward, and took about 12 hours to complete. I figure one third if you know what you're doing. But we took our time and tried to document everything.
Nothing was really stuck, or cause too much problems. For clearance, we removed the cross-over IM, which I had learned from before is a real pain.
It came as a surprise that the radiator also acts as an ATF oil cooler. This could be a problem, as I had intended to keep the W460 radiator. Unsure yet as how to make the W124 radiator fit.
We ran into one slight problem. The OM606 is a rather big engine, and with the tranny bolted to it there was a problem getting enough angle to get it out of the engine bay. We could've shortened the forward lifting chains, but that was a bit too late with the engine almost out.
This was solved by cutting some metal. The forward hood stiffener seemed to be riveted in place, and as the car itself isn't a keeper this was a bit quicker...
Yay, we got clearance!
Success, one down, one to go!
