Not sure about the maker (GMC or Chevrolet or GM), of the trumpet type of horns you are referring to. I have seen these on a few 41-46 Trucks. However I found the type of horns that you are referring to.
Matched Dual Horns. Chevrolet Master Parts Catalog Group # 2.218
General Motors Part Number #985610.
See scan below for factory accessories, as for install, I have seen nice and crude install of these. Must have been installed either by the dealer or local repair shop, or even the owner? Thereby causing different types of hardware, exact location, additions of horn relays etc. I sure would like to find the factory/dealer install instructions.
[IMG]
http://i391.photobucket.com/albums/oo352/46Canopy/MatchedDualHorns.jpg[/IMG]
[IMG]http://i391.photobucket.com/albums/oo352/46Canopy/th_46Accessories.jpg[/IMG]Edit: Add Cover scan of 1946 Accessories data Book. Horns are made for 1946
Good luck,
Dale
