Simrick and everyone else,
After considerable time spent going down several rabbit holes (and a lot of travel for my job), I got serious again about doing this Win 10 upgrade. First time, same flameout at 22%, but with a different error message this time. 0x800703f1-0x2000a. Doing some searching, I kept on getting links for registry corruption.
So I spent time trying out different registry cleaners. Then I installed the free version of CCleaner. Wowzers. Almost 1400 issues, way more than any of those not-free registry cleaners. In a way not surprising, since this Windows 7 image has been in service since early 2012 and I've gone through many software installs, uninstalls, upgrades, trials, you-name-it.
After running CCleaner, I was successful with the Win 10 upgrade. Woohoo! I'm happy. The sun is shining again. Time to change my sig.