What started as a backyard demolition project early summer led to one Michigan man unearthing a trove of bowling balls. David Olson, 33, hails from Norton Shores, in Muskegon County, where Brunswick Bowling Products was once a booming enterprise. The manufacturer—once boasting 11 factories in town—produced balls, pins, and other bowling equipment, as well as non-bowling products such as toilet seats and truck tires. Olson’s striking haul was not entirely out of the ordinary. It began with a project to clear some concrete steps: “We had a home inspection, and they had noticed that the cement stairs, on the top of that, the cement pad was leaning into the house,” Olson told MLive. “So, when water would drip on it, it would drip down into the foundation.” He set about removing the concrete. And soon he found a bowling ball. As he cleared more concrete, he realized that the entire pad was …