Exactly 70 years ago this Sunday—the day on which the largest U.S. sporting-event crowd since the onset of the pandemic will assemble for the Indianapolis 500—a 14-year-old kid from suburban Cleveland headed west with his father to watch what was then called the 35th International 500-Mile Sweepstakes. Roger Penske and his dad were late arriving at the central Indiana home of the elder Penske’s business associate, for a prerace lunch, and everyone had already left for the track—but before the Penskes headed out they took notice of a show car in the backyard. Roger pulled on a helmet, sat behind the wheel and posed for a photo.