I dont think other piston sleeves will work in that set up. But i have put a Ws7II piston sleeve in my S7 and that thing rocks!!!!!!!!!!!!
it's cheaper to get it pinched than buy a new motor. I have went tru more than 5 motors in 2 seaons of racing, and had them all pinched and they are as like new now. I bought the tool from ebay, instead of used rayracing, and after a few tries i got them right perfect..