By Andy Greene Early this year, Chris Cron — a Nashville-based vocalist who performs in the Beach Boys tribute group Pet Sounds Live — received a phone call from Beach Boys musical director Brian Eichenberger that left him almost too stunned for words. “He said, ‘Bruce is retiring,'” says Cron, referring to Beach Boy Bruce Johnston, who joined the group in 1965, and has played more than 6,000 shows with them over the past 61 years. “‘And we need someone to fill his spot. Are you interested?’ The offer didn’t even make sense to me.” For Eichenberger and the rest of the current Beach Boys touring band, led by founding member Mike Love, the offer made a lot of sense. Cron’s Instagram feed is packed with viral videos where he re-creates vintage Beach Boys harmonies with stunning precision, mimicking the unique vocal styles of every single member.…