The carburetor would be finished as follows:

Cast iron throttle body - black oxide
Bowl and air horn castings - chromate (NOT di-chromate) IMPORTANT: the chemicals used require an EPA permit, and are known to be both carcinogen, and capable of causing dementia. DO NOT ATTEMPT THIS AT HOME! There are companies that have the capability of doing this. At the present time, I do not know who, as I have not needed them for a number of years.
Steel items (throttle arm, links, screws) - yellow zinc or yellow cad

The above is true for 1951.

Sometime in the 1955~1956 time period (yes Virginia, there is an overlap on different carburetors), Rochester changed to black oxide finish on the screws, but retained the yellow zinc/cad on the other steel items).

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop