My '03 LT-Z400 is Street Legal in AZ. Alls I needed to do was mount 1 mirror. Wire up an electric horn and mount a license plate frame w/ light. It came from the factory with a rear brake light, otherwise I would've had to do that too. Cost me about $60.00 in parts and $122.00 to register it for the street for 1 year. It was pricey but it sure is fun to tool around town.
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ATV's 5 years old or newer don't need to be smogged either (in AZ). It may not help you for Ohio but it might give you an idea of the parts needed.