Hello everyone -
Update: Many thanks to Matt Miller for the tip on usermod options. That worked very well! I did not know those options existed and would never have thought to look for them.
After making and testing backups, I started with my main workstation. Rebooted in runmode=3, then ran the usermod -u and -g options. I did this in two runs. I first had to uninstall docker since it had taken over GID=1000. No big deal, I am not using it. After the usermod programs ran, I then did a "find -uid=500" with an exec option to change ownership. Repeat for changing GID. It found a few dozen files that were not in my home directory.
Rebooted main workstation. Everything came back up, no errors. So far after about a day of use it is working just fine.
On the server I ran the two "find" commands against the entire file system. It took about half an hour to run. No surprise there as it was finding and changing several hundred thousand files. I ran the uid change in one terminal and the gid change in another. Between the two of them they consumed about 90% on both processor cores.
I did not reboot the server since I made no changes to the user account on it.
Testing from several workstation - everything gets the permissions I expect. A few odd things that used to get blocked are now working. WooHoo!
With all that done I made a fresh complete backup of the server. That backup should have all the new uid and gid associations in it.
Next step is to revert to more sensible permissions. No more 777 and 666. That will take a while. It's not critical, so I will do it in spare (!) time.
Thanks!