There is another way to go that has not been discussed and trashed, that is a total conversion to a Vtwin of your choice turning a generator that powers an electric drive rear wheel. Eliminate the Centa, clutch, transmission, driveshaft, bevelbox, and rear drive belt and sprocket and put an electric motor on the rear wheel.
Smooth power and an engine that is readily available, like a MotoGuzzi, Harley, Honda, etc.
Don't forget you will need an HV battery and an inverter for the drive motor
