LYNN-He trotted his gargantuan dog Hercules around the television talk show circuit six years ago. Now John Flynn is competing for an American Power Lifting Association bench-pressing title.Flynn competes today in Keene, N.H. for the master’s title. He is confident he can beat the current record of 485 pounds.”I’m looking at 500 pounds. I’ve been training with the support of my competition sponsor, M&S’s Landscaping.The record Flynn hopes to beat is incidentally roughly the weight of his late English mastiff, Hercules, who was logged into the 2001 Guinness Book of World Records as the world’s largest living dog.The oversized honor made Flynn and Hercules stars of a sort. Flynn showed off Hercules at the Topsfield Fair and appeared six years ago on the Today show followed by other national TV appearances.