Mo. Rev. Stat. § 306.560

The provisions of sections 306.530 to 306.575 requiring registration of outboard motors in the office of the director of revenue of this state shall not apply to manufacturers or dealers in new unregistered outboard motors; nor shall it apply to nonresident persons who may be visiting or vacationing in this state for not more than sixty consecutive days at one time, or to outboard motors used on motorboats designed and intended solely for racing while competing in any race previously approved by the water patrol division in accordance with section 306.130, including operation within a twenty-four-hour period prior to such approved race in order to test or tune up the outboard motor.