An honor guard of motorcycles and police cruisers escorted a truck carrying a twisted 1,000-pound, 14-foot-long steel beam from the World Trade Center to the American Legion Hall in Amagansett on Aug. 13, in the culmination of a long effort to erect a 9/11 memorial there. For Tony Ganga, commander of the Sons of the American Legion Squadron 419, and for others involved in the planning, the artifact’s arrival was a cause for celebration.