Finally I gave up trying to fix the trim (you would see the cracks anyway no matter how carefully you glued them) and I just affixed the mirrored glass in place with an acid-free double-sided tape. That stayed there perfectly with no discoloration of the mirror for now about 15 or so years. But with the other restoration work going ahead well I decided to give correcting this a try too. Here is the result:
The how was amazingly simple. I just found some heavy copper wire with a white insulator. I carefully bent it to match the inside curve of the mirror, cut it with a sharp double bladed wire cutter (to avoid squishing the wire), and put it in place. I cut the wire about 1/16 of an inch longer that it appeared to require and thus the pressure it places on itself keeps it in place with no added help.
It may not fool the judges at the a Concours d'Elegance at Monterey, but so far I haven't had an invite to that anyway.
-don