Son of a Gun BSA - Just saw this, and immediately had to post. My god. My eyes are wide, and I think I’m drooling. This bike is based on a BSA Gold Star, and the engine is an ex racing 1951 XB-model single with 499cc.
Thumbs up indeed, dude. Well played.
Read more about this amaaaazing custom from my friends at BikeEXIF. :)