The scallops were painted and were not random. There are different patterns for different years and Meriden did use paint masks. The pinstripe was hand lined and differed between tanks in width. Different masks resulted in slightly different scallops within a model year. Unless your scallops are black or white a decal would look terrible. The tanks were usually candy paint over a silver, gold, or white base. A decal would have none of the depth that candy paint has.
Scott