A potential problem with Super Sixing my 1973 Duster.

Main reason is the choke horn (top of carburetor) is "fatter" on the 2 barrel than the 1 barrel.
Looks like you're running the earlier version of the BBD? Some people called the newer version the "tin top" BBD. Those came out in around 74-75ish. Nothing wrong with the older version, just don't see them as much anymore