By Tobias Carroll It’s been 20 years since the first Porsche Cayennes began making their way around roads across the world. As the German brand’s first SUV, it quickly became their best-selling model and was a harbinger for the rest of the industry. This week, Porsche opened up its archives to revisit the Cayenne’s history — and, in the process, revealed an alternate design that might have made for a very different driving experience for the first generation of Cayenne drivers. To be more specific, it would have involved a driving experience with the top down. As Porsche revealed, among the de…