The Fastest Guitar Alive (1967)

Confederate super-spy Johnny and his partner in crime Steve travel to San Francisco near the end of the Civil War, masquerading, respectively, as a singer/guitar instructor and a magic-elixir vendor. Once there, Johnny dons a fake wig, beard and mustache, and steals Union gold to bring back to the South, aided by a guitar that doubles as a gun.

Unfortunately the movie The Fastest Guitar Alive is not yet available on HBO Max.