Got it. The settings cited above are all correct. Delete CNAME, add .nojekyll and the url/baseurl settings in _config.yml are all good.

what I was missing was relative paths to links, css files, etc. After a massive search/replace operation, I now have it working on the local test site as well as the remote on GitHub Pages.

If you're interested: https://rontarrant.github.io/gtkDcoding/