Eureka! Problem solved and game is running in 16:9 widescreen format. After tooling around Google and burning some brain cells, I searched and found a solution: reinstall the Direct X files. I first tried using the DX9 installer on the game disc but that didn't work, so I found a 2010 version online, ran the installer, used JSGME to install the standard widescreen GUI in the mod list and ran with it, and it works! Game seems to run fine.
I am now a happy camper. Much gratitude to all who have helped me through this challenging process.
And now if you will all excuse me, I've got an uncontrollable urge....
"Ja ja ja ja, ja ja ja ja ja ja... Got an urge, got an urge and it's out of control...." to play SH3!
Auf wiedersehen, kameraden.