Electric vehicle startup Tesla Motors’ $226 million IPO in June marked the first debut by a car maker on Wall Street since Ford Motor began public trading more than half a century ago. Now two months later, century-old Detroit automaker General Motors, having emerged from government-managed bankruptcy, is gearing up for an IPO of its own and is widely expected to file its prospectus with financial regulators this week for a planned IPO in the fall (shortly before its plug-in Chevy Volt goes on sale).