Jeff - Just a little update since I had some time before the sun came up this morning to do a bit more research through the resources I have access to.
After reading through GM Heritage documents, Parts books, Maintenance manuals, a 1937 Chevrolet Truck Owners Manual and Chevrolet Tech and Service bulletins, the only reference I could find to rear axle "auxiliary springs" points to them only being available from Chevrolet for the 1-1/2 ton truck line models. Some screenshots below point to the basic info I found. The reference in the owners manual doesn't say which models the special equipment auxiliary springs apply to, but the listed spring rate matches the ones listed for 1-1/2 ton trucks in the
1937 Chevrolet Truck PDF from the GM Heritage Center files.
It is very possible that some aftermarket company offered overload springs that may have been installed on your '37 GC, or they could be adapted from later Chevrolet 1/2 tons as we can confirm many 1941-46 trucks have had them???
If the mounts and springs are Chevrolet items, somewhere they will most likely have a casting number that might help us trace them down. Until then, Happy Holidays!
