Dion DiMucci was just 20 years old but already a chart veteran when he went solo at the dawn of the 1960s.  Enduring hits like “I Wonder Why” and “A Teenager in Love” had been recorded with his friends The Belmonts, but when Carlo Mastrangelo, Angelo D’Aleo, and Fred Milano wanted to emphasize doo-wop harmonies and Dion wanted to rock and roll, Dion and the Belmonts split. How would the Italian kid from the Bronx follow that amazing first act?  The answer was “Runaround Sue,” the chart-topping record which established Dion as…