An update: These ~82YO eyes and brain finally happened into a realization that this ignition switch is identical to all others they have encountered. This is a well designed/pretty unit with the black on black retaining ring nearly impossible to detect (remember the ~82YO eyes and brain), but it screws off just like most other switches. It is an easy fix.
So God willing, and with warmer weather, I will complete this job. Just not today.