Angie,
Your dual horns look a little like the Accessory Dual Horns shown in the 1946 Chevrolet Truck Data Book. There was a City/Country horn selector switch with this unit (soft for city and loud to wake the country animals - "complies with anti-noise ordinances").
1946 Accessory Dual Horns It looks like the set came with a fender-to-fender cross-brace (referred-to by JiMerit)?
There are no optional or accessory horns shown in 39-41 Truck Data Books (but they still might have been GM options/accessories available from a dealer, or after-market horns from elsewhere). There were most likely no domestic Truck Data Books available during WWII. If you are really interested in what might have been available from a GM dealer,
a 1939 Accessory Price list will at least have the name. The
1938 or 1942 Sales Brochures might show options/accessories.
