More progress getting Sarah's standup/sitdown workstation sorted. Her birthday is next Saturday, and I am confident I'll have it installed before then. Below, see the laptop shelf at right next to keyboard mouse tray. When installed the shelf will actually be on the facing adjacent wall, at 90deg. Height adjusted for both fixtures using 5/16" bolts with nuts press-epoxied into wooden knobs.
the keyboard shelf is hinged with an original door hinge from the house that was removed during remodel. It's a gorgeous old Stanley sweetheart brass thing. Kind of sloppy motion for this application, but I enjoyed reusing the hardware for this. Notice the tension knob is recessed into the keyboard shelf. Normal operation would require sarah to remove the keyboard/trackmouse from the tray when folding up, but that's OK.
The laptop shelf has a full 19" of vertical translational movement because it also serves as a perch for the laptop when seated. It's best to not hunch over when looking at your lap top, and by elevating the screen to eye level, it should foster good posture.