you can stuff a piece of soft rope (I use spare pull start ropes removed from weedies) in the spark plug hole to stop the piston but if the hub is left hand threded on, it most likely has a hard loctite on it so you might as well leave it how it is

it looks like a Kioritz, most likely was just set up for a manual advance ignition, that's what it looks like anyway. you should be able to get a RCEXL ignition and just set it up on the magnet in the hub and just ignore or remove the auto advance ring.