Quick update for those interested....
If you are buying an engine from outside the US and want to import it legally, be prepared to go through some governmental type Red Tape.
Until recently, I would not have guessed that I would be on a first-name basis with anyone at the United States Environmental Protection Agency. However, through the process of importing this Mercedes OM604 engine, that's exactly what has happened.
Yes, it's a hassle, but I did everything "by the book", 100% legally, and won't have to worry about the Feds ever coming after me for having a non-compliant engine.
The engine is not yet in my hands, but has cleared customs.
Steve.