This end-view of a dual inlet OEM Holley shows smaller 5/16-inch inlet fittings; aftermarket dual-inlet Holleys were fitted with 3/8-inch inlets. Note the choke linkage is identical to original, too.
Right below the part number is the word "LIST," followed by a 4 digit number that may or may not also be followed by an additional number or letter suffix. While the letter "A" suffix shows up consistently in the Holley numerical guide, it rarely appears on the air horn. The Holley tech folks claim that an "A" indicates the carb was intended for "original equipment manufacturer" (OEM) use. The suffix "AAS" infers that the carb was a service replacement carb, and the "AA" and "AAA" were assigned to aftermarket replacement carburetors. Apparently, number suffixes (1, 2, etc.) indicated that a production change was effected on that carb application.
This end-view of a dual inlet OEM Holley shows smaller 5/16-inch inlet fittings; aftermarket dual-inlet Holleys were fitted with 3/8-inch inlets. Note the choke linkage is identical to original, too.
Single inlet OEM Holleys will have a 3/8-inch inlet fitting and the float bowls are of the side-hung variety. You'll notice even the OEM - spec'd bowl vents are present on this new reissue.
Basically, the 4 digit dating system is based on the Julian calendar. The Julian calendar assigns 001 to the date January 1, and continues on through 365 for December 31 (366 in Leap years). So, the first three digits indicate the day of the year while the last digit reveals the year of production.
Since all air horn stampings were a manual operation, there is always a possibility of error. You should take the necessary steps to ensure that the carb you are considering is the correct one for your Chevelle.
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