How this web site was set up
Dave Schweisguth registered fix26.org on cheap-domainregistration.com. That domain is configured there as follows:
It is forwarded (i.e. HTTP-redirected) to https://www.fix26.org/.
www.fix26.org is a CNAME for ghs.googlehosted.com. (Google does not document this well and it took a while to find.)
It has a DNS TXT record which proves to Google that Dave's Google account owns it. Dave had to generate the DNS TXT record in Google Search Console ― not in G Suite admin, which is where the Google Sites help sends you, or Webmaster Central, which is where the Custom URLs dialog in Google Sites settings sends you!
The fix26sf Google Site is configured to have www.fix26.org as its canonical "Web Address".
Much of the above is documented here.