Task completed without skin loss.
If anyone ever sees this: note the clips in the side surrounds pull straight out, and not upwards as all the images and manuals suggest. A spudger might help unclip the three across the top of the piece - they look like they are designed to have a spudger push in and lever up to release the lock. I used brute force, got lucky nothing broke. After it was off, it was obvious what I should have done.
Everything else was easy.