Well, it works now. And, I'm not quite sure how I did it. But, I'll try to explain...
Somewhere in the new control panel, I found a place to change what features display. I added "set custom resolutions" (or something like that).
I switched to classic view in Display | Settings | Advanced.
I told it to NOT hide settings the monitor doesn't support.
Several attempts at adding the 1680 x 1050 resolution failed.
There was an advanced button that was disabled. I think I enabled it by experimenting with resolutions from the list.
Clicking on that Advanced button, allowed me to add the resolution. But, coming back out still didn't show it as an option. So, THEN, I tried the Add button again. This time it accepted the custom resolution, and I was able to set it.
I don't which (if any) of those things did the trick, but it's working now.
Thanks for your efforts.