Forget the idea of putting one in a 123, or any MB for that matter, even if you can find one. I had a '77 2WD Chevy Blazer that I had repowered with a 5 cylinder 912 Deutz engine in the early '80's, just as the first 6.2's
became available. Deutz sold the engine and transmission, a Borg Warner
T-19A close-ratio 4-speed, and the Webasto heater as an EPA certified engine intended for use in bread trucks. The 1980 cost was $7700. The Webasto heater was used to supply cab heat, as there was no practical way way to remove heat from the engine, and there wasn't much to start with. This is why the original Iveco never took off, but the idea of a small cab-over had been planted in this country, and the Japanese proceeded to eat their lunch with the Isuzu and Mitsubishi trucks.
The engine weighed right around 1000#, was 287 cu in, 108 hp and 215 ft.lb. of torque. It was rated at 2800 rpm. It just barely fit into the Blazer, and I had to replace the front springs with those from a 2500 series Suburban. The good news is during the era of 55 MPH speed limits, it would deliver 34MPG in highway driving, and was dead reliable- never left me stuck in the 14 years I owned it. I haven't spoken to the person I sold it to for some time, but I wouldn't be surprised if its still running. The 912 and 913 series Deutz engines were built like a 123 MB- so you can imagine what one would cost today.