WASHINGTON (Reuters) - Lockheed Martin Corp unit Lockheed Martin Aeronautics Co is being awarded a $743.17 million modification to a previously awarded initial production contract for F-35 Lightning II Joint Strike Fighters, the Pentagon said on Monday. The modification also establishes maximum prices for one F-35A aircraft and one F-35B aircraft for a non-U.S. Department of Defense participant in the F-35 program, the Pentagon said in a statement.   