AV8TOR looking at the Pic's the outside Dimensions of both Crankcases appear the same. Bore / Hone the smaller inside case to fit the larger/better Reedplate/carb if the Vibes are really bad take a long crankshaft cut it down to size or just use the longer Crank in the Engine and check for Viberation. If you chose to do any/all of these Sugestions post the Results Please. Doug.