Shelby Flying Cloud. Based on the lettering on the brake arm, I believe it is a post-war bike. The chain guard is a Shelby, but for a 20" or 24" bike. You know you're on a big-boy bike when riding this bomb.
I remember riding a 1920s ish shelby 26 inch track racing bike that was covered it rust. Oh, It also had been modified with a coaster brake hub. That was a fun bike to ride, sadly it wasn't mine.