Why would you want to? FRS is designed around the gearbox that is fitted to it from the factory with ratios, diff, etc to suit. Similarly the ST170 has a 6 speed box with totally gear different ratios to suit that car. Put it in the RS and you'll change the way the RS drives and how you drive it, although if you want a 6th gear for cruising on motorways then maybe thats the way to go