John Red Shea, 40, was a top lieutenant in the South Boston Irish mob run, led by James Whitey Bulger. An ice-cold enforcer with a red-hot temper, Shea was a legend among his peers in the 1990s South Boston, as much as John Gotti, Bugsy Siegel, and Al Capone were in their time and place. When the actor and producer Mark Wahlberg, raised in nearby Dorchester, learned of a script based on Shea's life circulating in Hollywood, he immediately committed...