These were model WCFB and were like but slightly smaller than the common WCFB used on the "power pack" 265 and 283.
The carbs for the 2X4 corvette were stamped 15/16 on the bowl near the venturi and the common 4 barrel carb was stamped 1.This was seen looking down through the air inlet.
The 2X4 carbs would be scarce and pricey when you find them---the power pac carb is a lot more common.
57 and later had a velocity valve in the secondaries that the 55-56 didn't.This would be desirable on a street engine to delay the secondarys opening at a too low RPM.
No all mine have a good home and are not available.
Just thinking the early Buick (straight eight), Olds and cadallic used the small carbs with a smaller flange but otherwise same carb until the big flange(mounting flange) came in in 55.
Also Ford, Lincoln, Mercury had a small flange small carb until 57 but I didn't love those things with the float bowl up in the air cleaner---looked like a GM throttle body injector.

Bob Taylor