(Reuters) - Italian automaker Fiat SpA's shares could double in the next two years as it integrates its Detroit-based Chrysler unit and benefits from synergies in design, engineering, and supply chains, financial weekly Barron's reported in its January 6 edition. Fiat's operating leverage will get a boost from the U.S. economy's continued recovery and an improving outlook in Europe, according to Barron's. Fiat shares closed down 2.3 percent at 6.76 euros on the Milan stock exchange on Friday. (Reporting by Phil Wahba in New York; Editing by Jeffrey Benkoe)