No, the rear Supra struts won't fit on SC rear springs. The difference is the spring perch on the strut. By using this mixed combo, you'll raise or lower the rear car. I forgot exactly if it'll raise or lower it. There's not much of a difference in the spring rates between the 2 cars, given the same type. The quality is on the manufacturers, the spring rates that match your driving style, or the shocks..etc.
I got a friend who's willing to sell his used Eibach/Tokico combo for the SC. He's looking for a Tein Flex coilover. If you want, I can tell him and he'll give you a good price on them.