FALL RIVER — Some nights beg to be called perfect. Thursday was one of them. The Narrows Center improved on perfection with a summer block party held in the center of South Main Street downtown. More than 1,000 people gathered to see the bands Girls, Guns & Glory followed by Buckwheat Zydeco on a stage set up in the middle of the street, right between the Fall River Justice Center and Cafe Arpeggio.