Although Offenhauser never made a 2×2 intake for the Buick Nailhead engine, part number 3413 (3×2 manifold for 1953-1956 Buick Nailhead) was designed to be used as a 2×2 manifold by blocking off the center carburetor with part number 1097 (3 bolt carburetor block off plate). Dan at White Owl Speed Equipment has the manifold and block off plate. He can be reached at email@example.com or by calling 559-786-1864.
Thank you for your answer , I am in contact with Dan now. You helped a lot.