The 216 used an S.A.E. size 2 flange (center to center 2 11/16 inches).
The 235 used an S.A.E. size 3 flange (center to center 2 15/16 inches).
There are various internal venturi sizes for each flange size by most carburetor manufacturers.
Both Stromberg and Zenith were owned by Bendix. The same engineers designed carburetors with both the Stromberg and Zenith name. This is because prior to about 1920 (don't recall the exact year); both Stromberg and Zenith were independent companies. Bendix made the decision to allow both nameplates, and each division (company, whatever) retained existing customers; although Bendix would attempt to direct new business as Stromberg getting the passenger and light truck, and Zenith getting the industrial and heavy truck. There are always exceptions.
Stromberg and Zenith carburetors with the same S.A.E. flange AND internal venturi made in the same time frame will flow exactly the same.
Jon.
