I hadn't heard from anyone by the time I started early this AM, and had to learn by doing. Wish I had waited a couple of hours, it would have gone quicker.
You are right, there is a big difference between door panel mounting in 123's and 126's.
I can add only four minor things to your excellent instructions:
1: when removing the snap-in panel behind the inner door latch, start at the front; a finger nail might do it, but if not, use a fairly dull knife and take care not to scar the bezel. The snap-in panel is very flexible.
2: when re-installing it (snap-in panel), make sure the tab at the rear is aligned properly with the slot in the bezel and that it is neither in too far (all the way under the bezel) nor not in far enough (it can be snug without the tab in the proper place, in which case the latch handle will forevermore scrape on it) before pressing the front in.
3: when removing the screw under that snap-in panel, try not to let the (nearly invisible) star lockwasher escape.
4: the seat adjustment knobs in the rearmost control panel pull off as you might expect, but the little plastic c-clip that must be removed from around the fore-aft control center-post is also difficult to see, and will attempt to escape, like the star washer.