The Holley 1901 was a 2 barrel 'Concentric' carburetor, similar to other 'Teapot' carbs such as the Holley 2140-4000. Holley 1901FF's were used on Mercury engines on Ford and Mercury cars, as well as on the 1952 Lincoln.
Holley concentric carburetors are sometimes referred to as 'Teapots' because they consist of a throttle body assembly with a float bowl suspended above. There are both 2 and 4 barrel models, and the basic type was used on cars from 1949 to 1956 and on trucks well after that. Governed 4 barrel concentric carbs were used on IHC trucks into the 1970's.
Model 1901 carbs are stamped with a Holley LIST number on the rear of the base of the carburetor, usually along with a Ford number as well. How to find Holley carburetor list numbers