I've learned a great deal from y'all sharing your knowledge and experiences. I even stumbled on one very impressive auto tech YouTuber who mentioned in passing that as little as 1mm on rear brake shoes is meaty enough for more driving miles before replacement is necessary. I don't think I have enough courage to go to 1mm, yet this does help me gauge my current 3mm condition.
All considered, I do now have a game plan that includes adding a routine backing-and-applying-the-e-brake to my driving regimen and ordering parts (including drum gaskets) for eventual replacement of shoes, and maybe even the drum. Time will tell. I am, with this new knowledge, looking forward to doing the brake job.
This has been a very positive learning experience for this 80-year-old, long-ago-retired high school principal.
Thank you gentlemen one and all.
Greg