Got a a 13.5 Novak mongoose system in a 18r right now and I never use it anymore. Thinking of buying a sc18 to race around my neighborhood and ocrc mini track on a 3s lipo. How much is a roller? And do the steering slop still apart of the 18 line? (IE bad servo saver)? Also will the mongoose fit in? As well what is this whole from diff deal?