Was still having problems with Windows update not completing, so I checked and repaired the disk image per guidance found at: https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-8.1-and-8/hh824869(v=win.10)
After that Windows installer began working correctly again and I was able to install VS Community and some other apps which I had been having issues with.
All is fixed now - thanks for your help pointing me in the right direction!