Thing is with something like this there's gonna be saftey and legality issues. Some states have laws that anything above 80cc (some states 50cc+) require for you to have a motorcycle license to use it for road use.
Also you'd have an issue of safety. If your brakes suck already (even if they were great) you're talking about adding about 42lbs of weight which is a lot to balance on something that small. Also the power/weight ratio, frame modification, and possible damages otherwise. Massive weight change over rear axle would change the gyroscopic properties and severely upset the balance, also cause issues with steering and front traction in general. You'd be better off finding a mini bike on craigslist or FB marketplace ads and slap the engine on that.
All in all what you're talking about is highly in unrecommended and could cause serious issues/injury.
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