At the current moment, I have the ICE engine out and the Razor motor in and wired up. Using a small hub on the 500 watt motor, I'm getting about 5-8mph and not nearly enough power to make it up hills. Fortunately, this was designed as a moped and I can pedal assist whenever I need to. Also, the centrifigual clutch means I can't stall out the motor.
My partner had bought an old Piaggio Boxer mo-ped a couple of years ago but sitting in our garage had rusted out the engine. I decided to make it an EV conversion.
So far, I've removed the old ICE cleanly. It looks like the ICE was connected to the rear wheel through a belt-driven CVT / clutch.