Rob Kauffman opens the door into his automotive showroom, and it is hard to know what to drool over first. Corvettes, Mustangs, Camaros, Firebirds—250 or so of the greatest expressions of speed, power, and ingenuity Detroit ever produced—glow as if they just rolled off the production line. Some of these cars are in Kauffman’s personal collection; the rest belong to RK Motors, his vintage car dealership in Charlotte, N.C. As Kauffman cuts left and walks toward his personal cars, the first one that commands atte…