Peter:

The block design of the four and six cylinder engines of the 60s and 70s was very smilar to the diesel engine block design. I certainly could mistake a gasser block for a deisel block without the heads on, and the cranks don't look that different, either.

Remember, Benz was a fairly small concern in those days, engineering talent was spread a bit thin. If the desgn works well, modify it a bit. You could drop a dizzy right onto the oil pump shaft of the OM 61x engines without a bit of trouble, and I'd bet there is a nice flat spot next to it for the bolt hole for the holddown!

Obviously, they cannot be interchanged, I don't believe, but they are very close.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!