I just installed a knife switch to disconnect battery on my '41 GMC - purchased from NAPA.
knife switch battery disconnect


1960 GMC 1/2-ton Fleetside
"Donald"
In the Stovebolt Gallery
More pix on Flickr

1941 GMC 1/2-Ton Short Box Stepside
"Wilburforce"
In the Stovebolt Gallery
More pix on Flickr

1943? Chevrolet G7107
1946 Dodge COE 1-1/2 ton
1939 Allis Chalmers model "C"