Ford 4300 carburetors were used from 1967 to 1974. Model 4350s were built from 1975 to 1978. The model 4300 has a velocity valve below the secondary venturis. The 4350 has a air valve above the secondary venturis. Most 4300 carbs used a square bore, Holley style flange, with the secondary and primary throttle plates about the same size. Model 4350 carbs have much larger secondary plates than the primaries and use a specific Ford flange. They can't be bolted onto Holley, Rochester or other 4 barrel flanges.
The model 4300D used the square bore Holley flange, but the secondary throttle plates are somewhat larger than the primaries. These appeared mostly on Ford 351C applications.
Ford carburetors are generally identified by the number on a metal tag. The carbs are variously marked as Ford, Autolite or Motorcraft depending on the year of manufacture. Model 4100 carburetors were also stamped with part of the carb number on the edge of the base, near the front on the throttle body.
Ford tags and stamps are discussed here.