Was at a museum this weekend and heard more about this motorcycle company from a curator. Henderson was purchased by Schwinn bicycle. It became a division of Excelsior Motor Manufacturing after the purchase (hence the X logo on the gas tank). Schwinn bought Excelsior just a few years before buying Henderson.

This is a 1931 Henderson KJ. Great review of these on Jay Leno's YouTube channel. It's a 4 cylinder. Leno shows how it even had a reverse gear!