1920 is not the carburetor number, it's the carburetor model. There were between 6 and 10 different Holley 1920s used for each of eleven model years' production (1962 to 1973), plus 10 different aftermarket replacement 1920s. Grand total of roughly one hundred different 1920s! Many design aspects and features came, changed, and went during that timeframe. That's why your question is not specific enough to answer yet. If you actually have the two carburetors (and it sounds like you do) then you can find the carburetor numbers by looking at the flat surface of the carb casting, above the fuel inlet fitting. The carb number is four digits, sometimes followed by one or more letters. For example, "2372A".

BorgW 10392A

Thanks for everyone’s help on my carburetor acceleration problem. As Dan had suspected it was the accelerator pump plus a few other things I would have never figured out on my own.

At Dan's suggestion I sent it away to be refurbished. Dan suggested I send my Holly 1920 to Max at Buzzard Carburetor. www.buzzardcarburetors.com. Excellent suggestion Dan, Max was a true pro the carburetor came back looking brand new and all the issues were resolved. Max called me several times to be sure he understood exactly the issue I was having.

I bolted the carburetor on and the car started right up and runs perfectly. According to Max the rebuild kits available for this carburetor can have some parts that aren’t always correct, there was also an issue with the economizer assembly body and float spring. I only wished I had done this sooner.