When  Amtrak’s Northeast Regional train 67  crossed the Niantic River  on its nighttime  run from Boston to New York at 11:39 p.m. on September 7, 2012, it was the last train ever to travel on “Old Nan,” the 105 year old railroad drawbridge  between East Lyme and Waterford,  a historic “choke point” on the nation’s busiest rail line.  At…