A note on the 5mm hex key wrench:
My experience with the M103 in my R107 is that the fan has a different spacing between its blades. Hence you can get your hand from the engine side through a wide spacing and skrew the wrench from the front side of the fan. - Now, reading further, I find my comment in your description in step 2. So why did you mention the need of special tools for Allen bolts in the beginning?

Step 1:
I am not sure what you mean here (maybe because I am a non english speaker). However, what do you mean with head cover. Is this the camshaft cover?

Overall, a great article with expressive pictures!

I am collecting links to good articles (see http://www.thomconsulting.de/MB/mbtechnikverweise.htm and use an online translator) and will be happy to link to yours!

Best
Tom

PS: Could you post a wiring diagram of a 1990 W124 M103 cruise control, as I urgently need one?!