Paul Faltyn of the Niagara Aerospace Museum recently provided me with some Bell Aircraft artists concepts of a marinized P-39 Aerocobra.
This is verified by the illustration of a takeoff from an aircraft carrier.
Even more interesting, and hinted at by the extension of the carburetor inlet fairing evident on close examination of the first illustration above, is what appears to be a turbo supercharger in the following cutaway drawing.
The Allison engine incorporated a single-stage, single-speed supercharger. This meant that power dropped off after 12,000 feet, significantly handicapping its speed and climb performance relative to fighters powered by engines with additional supercharging
For what really happened with the Bell FL-1, see my monograph on the Airabonita published by Steve Ginter and also available from Amazon.