The problem is it’s fundamentally changing the source of energy in a car. Even if you ripped out the motor and replaced it with an electric motor and battery Bank there would still be a whole fundamental sleuth of systems that would be missing inside the car. I think I better solution might be to look into converting cars to hydrogen instead.
Also feel free to ignore anything I just said I’m not no automotive engineer, just a nerd who used to tinker with cars when he was younger 😅