Ive just bought a set of mag wheels for my 76 puch maxi 1.5 hp. When I received the wheels the rear sprocket was substantially different from the one that was on it before. The old sprocket will not fit on the new wheels. What are the most likely combinations for these types of set ups. Can i just replace the front sprocket and shorten the chain? What are the down sides of this? Any help would be greatly appreciated.