First, as Rochester made their first carburetor in 1949, you can easily see that no Rochester would be original for a 1946 truck.
I am unaware of any Rochester type "C" carburetor. However, Rochester would append a "C" to the end of the carburetor type to denote integral automatic choke. The type "B" carburetor has a manual choke. If it were used with an integral automatic choke, it becomes a type "BC". If used with a divorced (sets on the manifold) choke, it becomes a "BV" (the "V" chosen because of the vacuum choke pull-off required with the divorced type choke).
This same convention also used with the 2G (2 barrel) and 4G (4 barrel) Rochester carburetors.
Jon.
