Clear differences between the 998 and the current 997 model are a pair of more upright headlights, side mirrors positioned at the side of the doors and not at the window, and a slightly longer body. This particular test vehicle has some visible lines around the rear window, suggesting that it is removable. It is not clear yet if Porsche will only have AWD versions of the Targa like the current model, but tougher fuel economy and emissions regulations may see the introduction of a lighter RWD version.
It is also still too early to determine what changes Porsche has in store for the engine lineup, but expect to see the recently revised flat-six engine range carry over with only minimal updates – possibly for emissions and economy standards. The new PDK dual-clutch gearbox will also carry over as will a standard six-speed manual.
Source: Motor Authority