More photo references, 1951 set, the bracket are attached to the horns, they attach to the cad brackets shown. As discussed earlier wiring was made in exact, complete lengths.
https://www.flickr.com/photos/advance-design_parts_co/8129454392/in/album-72157631868452754/
Detail on the H (high) low marking on horns. High is always the optional horn if single set.
https://www.flickr.com/photos/advance-design_parts_co/14150816938/in/album-72157631868452754/
Typical dual horn install kit, all parts, pieces, directions furnished.
https://www.flickr.com/photos/advance-design_parts_co/15492567825/in/album-72157631868452754/
GMC NOS version (very rare as are most GMC accessories).
https://www.flickr.com/photos/advance-design_parts_co/16058087333/in/album-72157631868452754/
A set installed on a COE, pretty tight!
https://www.flickr.com/photos/advance-design_parts_co/28601771951/in/album-72157631870734114/
Pre-1954 vintage kit, identified by cloth wire.
https://www.flickr.com/photos/advance-design_parts_co/44122206874/in/album-72157631868452754/
1953 Accessory Guide showing single horn.
https://www.flickr.com/photos/advance-design_parts_co/23903473532/in/album-72157631872034068/
1954 Accessory Guide showing single horn.
https://www.flickr.com/photos/advance-design_parts_co/29345261632/in/album-72157631872034068/

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr