From Joe Baugher: 

Douglas “A-26Z”, A-26G, A-26H

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The designation “A-26Z” was an unofficial designation for a proposed postwar production version of the Invader. It was to have a more powerful version of the Pratt & Whitney R-2800 radial engine and was to be fitted with such features as a raised pilot’s cockpit canopy, an improved cockpit arrangement, and wingtip drop tanks. If produced, the unglazed nose version would have been designated A-26G and the glazed nose version A-26H. However, In October of 1945 the USAAF concluded that there were enough A-26 aircraft to meet any postwar needs, and the “A-26Z” version was not proceeded with.

Sources:

1. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.
2. McDonnell Douglas Aircraft Since 1920: Volume I, Rene J. Francillon, Naval Institute Press, 1988.
3. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.