don't want to the be the bearer of bad news but before you put any money and time into it...
http://www.thecarburetorshop.com/CarterFourBarrelCarburetors.htm
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AVS
Carter introduced the AVS in 1966. Chevrolet used it on the 275 horsepower 327. The acronym AVS meant “air valve secondary”. Basically, the first incarnation of the AVS was an attempt to place the “demand” spring tension secondary on the square-bore AFB style carburetor. From a manufacturing standpoint, much less expensive to produce the spring tension secondary than the weighted airvalve. Chevrolet used it one year, but then dropped the AVS in favor of the Rochester Quadrajet. Carter still thought it could work, and during 1967 did lots of R & D on the primary circuit, utilizing the 3 step step-up rods and some differences in the primary venturi cluster (remember the Clean Air Act of 1966, to take effect with the 1968 model year had just passed). Due to the really precise lower RPM metering characteristics on the revised AVS carburetor (useful for smog emission calibrations), Chrysler purchased them for use beginning with the 1968 model year. These carburetors were quite troublesome, and before the final demise of the AVS after the 1971 model year, the AVS sometimes didn’t last as long on a new muscle car as the first tank of gasoline! Most enthusiasts changed them out, either for pre-smog AFB units or for Holleys. Carter did make one final attempt to market the AVS in 1972, as they offered several aftermarket versions. However, these didn’t sell; if fact, I have never seen one!
A total 55 different models of the AVS were produced, in two different CFM sizes. The ones with both primary and secondary throttle bores the same size are 750 CFM; the others are 630 CFM.
All AVS carburetors that I have seen have been stamped with the identification number on the passenger side front throttle body edge. Some have also had the metal tag.
Since we will not rebuild the 1968 and newer AVS units, I cannot offer any tips on rebuilding."
