RE: Clutch for an O.S .18?
Usually the Traxxas can be gotten at an area Hobby Shop, the Mega-Tech might be harder to get. Take your engine along to make sure that it will work. What you'll be looking for is the one for the Nitro-Vee.
I'm not a personal fan of them but if that's what you really want, go for it. One reason why is that people forget that you have to keep water running through the head. Owners of clutch equipped boats want to play stop and go on the water.