The code numbers of a Holley carburetor are usually located on the side of the air horn. You will find that the Holley model number of the carburetor is there, along with the automaker part number if it is factory issued, as well as a date and application code. So you should look for the lone four-digit code.

It's like a "VIN" for your carburetor and should be hand-stamped on the front of the choke tower to the right of the vent tube on most typical Holley carbs. The list number typically is four to six digits long and may or may not have a suffix number behind it. The date code will be right below it.