Jason Arthur of Korea is a great fan of SBs. He spotted these photos of what he says was an SB-50 online.
He adds, “The serial is 2080510, which would probably date it to 1982. It looks like it might have a shorter scale than the throughneck SBs. But as you can see from the headstock and body shape it is definitely from the SB family. I'm guessing it's a domestic model that was never intended for export, probably entry level.”