Yes, this really seems worth a shot, if possible. If the old site was on a domain that you own, remove the CNAME to github pages, and point it instead to a ser

Yes, this really seems worth a shot, if possible. If the old site was on a domain that you own, remove the CNAME to github pages, and point it instead to a server you control, that returns 301 redirects to the new site. The 301's are a standard way to do this, while the meta refresh tags are dubious at best.