One year ago I tried to get info of the possible Perfect power SMT6 installation to my viggen. Back then the local distributor could not locata any T7 saab's that had SMT6 istalled to them. There were several T5 car, but that did not help much. Anyway I tossed the idea a bought a upgrade ECU because there weren't any garantees fron Perfect Power that their product would have worked in my car.
Usually piggi back systems are easier to install to older cars' because the sensor margins are alot bigger. I have heard that some cars wont even tolerate anything between the sensor and ECU. So if you go and istall a piggi back the sensor voltage will drop a bit and in some cases the drop is to much.