1957 was an interesting year for FoMoCo regarding carburetion.
In place of the Holley 4000 ‘teapot’ used in ’56 on 292s and 312s, for single quad application 1957 Ford passenger cars (312 engine only), Ford used the new end bowl Holley 4150 carburetor OR the new end bowl Ford (Autolite) 4100 OR the new Carter AFB. Single quad ’57 312 ‘Birds used only the Holley 4150 carburetor.
In place of the Holley 4000 ‘teapot’ or Carter WCFB (used on 2 [?] models in ’56), for single quad applications 312 y-blocks, ’57 Mercs used the new Holley 4150s or the new Carter AFB, in my junkyard experience.
Many Carter AFBs used on ’57 Fords and Mercs have the part number ECZ 9510-AA on the front edge of the aluminum base casting above the idle adjusting screws.
The vacuum chamber you mentioned adjacent to the choke housing controls the opening of the secondary throttle plates.
Hope this helps.