I have a '59 GMC ½-ton fleet option that has it on the firewall, a '59 GMC 2-ton dumper that has it on the passenger inner fender and a '55 GMC 450 with it on the firewall. All the trucks have 6 cylinder engines. I have no idea why there are differences.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.