Cheers!
Fragment of a discussion from User talk:Rua
Oh well. By the way, just wanted to check, is this Proto-Brythonic descendant form correct? https://en.wiktionary.org/wiki/Reconstruction:Proto-Celtic/Orbogenos
"g" definitely seems to become that sound, and the "o" becoming "u" is apparently explained in Jackson, but I don't own a copy and can't check.