Here's a link to some service manual info for the W123 sunroof.
http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Chassis/77-100.pdf If the link doesn't take you directly, go to the Skinnerbox main page (
http://skinnerbox.steaky.org/ ) and look under the W123 chassis button, pick an engine, then navigate to the section on roofs (77 Sliding Roof). It appears the other models are indexed but there is nothing in the text to view (but you could try - this is a work in progress I guess).
I have the manual for the W126 380SE in hardcopy. I'll try and find some info on your questions.
Edit: I checked the skinnerbox index for sliding roof against my W126 manual, and the instructions appear very much similar. I do have an additional section that isn't listed on the website called "77-300 Removal and installation of sliding roof frame", plus my copy has different steps for some of the procedures depending on whether the model is a coupe or sedan.