Originally Posted by Mike D

For a "straight" swap you need to source a pre-'76 N.A. OM617.910.

The engines used after '76 MY (W123) are the OM617.912 and other variants which have the oil filter mounted up high on the side of the block. An oil filter by-pass or conversion plate would be required.

ANY of these engines will require a modification to the engine shut down as the MW series injection pumps are used which use a vacuum system as opposed to the "Gorilla knob" manual shut-down and start type.