12v engine in 6v bike

Sorry to post about an old topic, but what is the best way, if there is even a way, to fit a 12v engine, such as a Lifan 125 into a 6v bike?

Easy bolt the engine in.
Swap the headlight and break light bulbs,
Fit a loom adaptor that lets to add a CDI https://www.motorkit.com/en/ignition/75 ... volts.html
if you have indicators swap the bulbs and flasher, then change the battery to 12 v