Nice! My first-ever siren was an S8 (no brake) like that with the small rounded motor. It was 6-volt and had been given to our Explorer Post by Dick Miles, Kevin O'Connell's mentor and predecessor. When the Post folded my junior year in high school I was given the siren. I had noticed that Cooper High in Abilene had an early Federal Director rigged up for football games; so I figured we could out-do them on that. I went to the principal and ass't principal and got permission to bring my siren to our games. My dad mounted the siren on a board with the foot switch that came with the siren, and found a decent 6-volt car battery. With some of my buddies helping, we became the Lee Rebels Siren Squad. Oh...that was a blast (literally)!
I just noticed: on your siren the rotor guards are missing. Could be they weren't used on that particular run of S8Bs. Super-nice looking, though. Good luck with the sale.