Legal question about Antique vehicles and the seat belt laws

Picked up a '63 Valiant near Des Moines last fall. The PO had done a complete restoration on the car. I went down from Minneapolis/St. Paul area to drive it home. No seatbelts. He said it didn't need them by law. Scariest drive back home on I35. It now has seat belts for my own comfort level. So used to driving with seat belts everyday, I felt naked without them.