Be sure you at least have a Bill of Sale between you and the seller. Most states will make an allowance when something comes from a state where a different item is titled. That can change based on the office or even the person you get at the state office. We find sometimes the requirements change even from person to person in the same state office. Makes it kind of a moving target. Every boat, motor and trailer gets an MSO (manufacturer statement of origin) when it is built. Those docs should be around someplace since they would not have been switched for a title. Mississippi has what is called an "optional title" for boat and engine. That NORMALLY means that if there is a loan. the lender would want that option. I know when we do loans in that state, we do the title work.
Always best to have the conversation with your state on the requirements.
Let us know if we can help.