You can use a single 2-barrel adapter to the single carburetor original intake - Whitelightening refers to one.
I have used two such adapters. 4-bolt 2-barrel to 1 barrel; and, 3-bolt 2-barrel to 1-barrel (which I am now using with a Holley AA-1 - same bolt pattern as Holley 94/2100/2110).
