The greater torque (nearly double) is one problem. The second is that the 50cc Honda has a shaft output, and not the standard small engine flat 3 inch (apx) clutch mount. So, in order to use the GEBE, you would first have to adapt the engine; Staton sells the adapter and clutch for about $130 (total.) However, it entails cutting off some of the shaft, then drilling/tapping a centered hole in the end of the shaft.
The engine is substantially heavier than the 35cc motors, and that, coupled with a motor that is wider than the 35cc motors (which places the center of mass for the motor farther from the bike centerline) AND being pushed even farther out by the adapter, could make the bike uncomfortable to ride...