stupidity has nothing to do with it. You DID buy a benz after all. You've just stepped off a small cliff into a realm that you have little experience in. We all did that at some point in the past. You're just one of the new arrivals.
OK, first question, A "D in the back of what?" You mean a "D" sticker on the trunk? People do that here in the US if they've visited Europe or had a relative visit and bring back a souvenir.
The parts book w/ numbers is almost unfindable. But is also rarely needed by somebody that just owns a car for their amusement (in spite of the fact that I have spent the past 3 years tracking down parts books on ebay almost daily).
What you really need, is the right glove box picture book, so that you can converse intelligently to a parts supplier.
The other thing you need is the factory service manuals. Look for the 108-109-111-113 manual, there are at least two on ebay right now. Don't pay more than 40$ for it. Also, that same manual is available on CD.
That one manual won't tell you much about your engine, but it will have all body & electrical stuff you need. If you can the manual for "models starting 1959...", also on ebay (get the paperback version) and again, don't pay more than 40$, you will have tons of good reading material.
Lastly, there is a plate on the door pillar that will tell you the year of manufacture (the 1970 model year cars were built starting june 1969). It has your chassis number. On the block, over the oil filter by a few inches is a flat spot. The engine number is stamped there.
There are other web sites to visit. Check out
http://www.mbz.org,
http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm and of course the archives here.
-CTH
PS. above all else, enjoy your search just as much as you will enjoy the fruits of it.