Classic - with all due respect, your last post is historically inaccurate.
Chevrolet DID use Zenith as original equipment..............................from 1912 to 1925 on a 4 cylinder 171 CID engine. These were updraft carburetors.
Chevrolet DID use Zenith as original equipment on their 6 cylinder of 299 CID......................in 1912 ONLY. This also was an updraft carburetor.
The last Chevrolet to use Zenith as O.E. was 1925.
Zenith did offer a replacement carburetor for the stovebolt 216.
Zenith did NOT offer a replacement carburetor for either the stovebolt 235 or 261
Zenith did offer a number of "universal replacement carburetors" of different venturii; and the customer was responsible for picking the correct one for his/her application.
GMC DID use Zenith as original equipment on many different size engines, and we have been recommending these GMC versions for years.
Jon.