Yes this is a Naturaly Aspirated diesel - the Turbos didn't come from the factory untill '...
Yes this is a Naturaly Aspirated diesel - the Turbos didn't come from the factory untill '82 (well in the smaller chassis' at least - in the form of a W123).
About the water separater, don't bother - they cause more trouble than good. Mercedes never offered one on this or any other chassis diesels. The fuel may be geled however, in which case you will want to add some anti-gel fliuds - can be purchased at any Marine or PepBoys type autostore. If you suspect serious fuel issues (I.E. water in the lines) then take off the pre-filter, drop the lines from the tank and drain the tank. The drain plug is at the bottom of the tank - it's quite visable from below. I would think that just some anti-gel and a couple of gallons of fresh diesel should get it going.
Oh, If you don't know how to pre-glow the pull starter cars (like your 220D): Pull the starter knob out all the way just before it catches the starter, and watch the small circular metal thing just above the steering column. There is an actual glow plug coil in there that will glow just as the ones in the engine do. If it will not glow - the 114/115 chassis cars had glow plugs in parralell (I think thats the one - either parralell or in series) which means if ones out, they all go out. Anyways - good luck and have fun (semi-)restoring it! It may seem overwhelming at first (if this is your first) but they come around eventualy!