If I recall correctly, all the 240D's in all the chassis variants had MW pumps. The 220Ds prior to 1974 had M pumps.
The main differences between the M and MW are the lubricating oil and the altitude compensation.
The M is the old style pneumatically-governed IP with a diaphragm that regulates fuel via a throttle body and venturi vacuum. Oil is internal, not connected to the engine at all. Kind of ingenius and insane design, if you ask me.
The MW is oiled by the engine, has a mechanical fuel governor and altitude compensator is a small vacuum can with diaphragm that reacts to ambient air temperature.

Phil Forrest

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1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson