Actually, Rochester was a Division of GM. GM made more money by using in-house parts rather than buying parts. As some wise person once said "Follow the money!".

But if one looks at the model production history of Rochester:

1949 - first carburetor, model AA used on Oldsmobile (Rochester took a trick from Stromberg, the double letter meant 2-barrel)
1950 - revised model AA used on Oldsmobile, and model B (single letter, single barrel) introduced on Chevrolet
1951 - model AA discontinued forever (thankfully!)
1951 - model BB (double letter, two barrel) introduced on Oldsmobile and Cadillac
1952 - model BB discontinued forever (thankfully)
1952 - model 4G introduced on a number of vehicles (GGGG would have been awkward, so terminology was changed to 4G, just as Stromberg used the 4A).
1955 - model 2G introduced on a number of vehicles.
1965 - model M (4MV) introduced on Chevrolet
1968 - model M (MV single barrel) introduced

So summarizing:

There was no single barrel version of the model A
The two barrel version of the model B was discontinued after 1 year

The model 2G was used from 1955 through at least 1974 (the latest information in my database)
The model 4G was used from 1952 through 1966
The model B was used from 1950 through 1968, but the two barrel B was discontinued after 1 year

WHY was there no single barrel model G?

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