Help with identifying an engine
 

Found this .21 engine while rummaging through some boxes of old r/c stuff. The only thing I can tell you is that it is a Rossi engine. It has 6T on one side of it as its only ID sign. I have no instructions on it, just the box and the engine itself. A friend of mine that left the hobby gave it to me several years ago. Need to know if it is an onroad or offroad engine as well as the model. Thanks.