Possibly not a lot if you bought the stuff of eBay second hand, but you would have to do a hell of a lot of modifying etc. Like shortening axle, figuring out how you would mount the brake to the stool etc. Also unless you used a comer cadet engine (small 60cc engine similar to a chainsaw engine) you would be faced with the deafening noise of a 100cc 2 stoke motor with loads of torque and there would be no place to mount the exhaust on a stool lol. If it was to be done id say go for a comer 60cc cadet engine as they have exhausts built into the rear of the engine, they are pull start also and nowhere near as loud and quite small. The brake and axle is going to be your biggest problem Id say....but iv seen your models so I’m sure you could come up with a way around it! They do actually have these that you can buy I think as there was a rich kid who had one when I raced karts - he used it to get from his awning in the paddock to go to the toilet cafe etc! Must have been 7 years ago now that he had one and that was very trick. I’m sure iv got a pic in a karting mag somewhere but iv got hundreds so god knows where that is lol. Cheers Adam