Engine demand strongly affects carburetor flow, all CFM is rated at a specific vacuum draw: 3.0 Hg" (inches of mercury) for 1 and 2 bbls., 1.5 Hg" for 4 bbls.
A smaller-than-calculated carburetor will only reduce peak power slightly (if at all), in part because the restriction raises the WOT vacuum slightly (above the 3.0 Hg"standard for testing).
A larger-than-calculated carburetor will only increase peak power slightly (if at all), in part because the restriction lowers the WOT vacuum slightly (below the 3.0 Hg"standard for testing).
Some mixture compensation for incorrect size can be made by jetting changes, even float level adjustments, but what's your time & trouble worth?
I'd try to get the right one.
