Hello, Neil,
Do you have a 1940 GMC Maintenance Manual?
Here is the pertinent section in the 1941 Chevrolet Truck Shop Manual.My guess is that GMC & Chevrolet trucks used the same parts in this assembly?
Regarding your request for parts: this type of request belongs in the Swap Meet.
Good luck with this repair. Keep asking questions - members will post advice and suggestions.
[I see you have already posted a Parts Wanted Ad here - good]