Listening to the radio is such an essential part of driving a car, and no more need be the days of endlessly twisting nobs, combing through the airwaves in search of an audible AM radio station with a bearable amount of static. Retro Manufacturing, based in Henderson, is the world’s largest manufacturer of shafted radios for classic cars. The company, founded nearly 10 years ago in Chino, Calif., moved here in October of 2013.