American pork exporters have spent years trying to ramp up sales to China, the world’s most ravenous pork market. Their sales pitch has been stymied by onerous quarantine rules, protectionist impulses, and chaotic distribution channels. After a jump in 2011, shipments to greater China dipped 3% by value last year to $886 million. Given China’s growing protein diet and widespread worries over food safety, there’s plenty of upside for quality pork imports. That’s why the deal announced Wednesday by Smithfield Food Inc, the largest U.S. hog processor, to sell itself to China’s top producer, Shuanghui International could be a game changer. If the takeover goes ahead, Smithfield would get a crack at the most lucrative slice of China’s market: chilled, processed pork for supermarkets and convenience stores. …