Unlikely. Most state and provincial laws in North America require that seat belts be present if the vehicle was originally equipped (or if the vehicle was made in or after a certain year, usually 1967). I can't think of any that require retrofitment of belts to vehicles not originally so equipped. But anyone who wouldn't retrofit belts in an older vehicle just because the law doesn't require them is a moron who should eject him- or herself from the gene pool as quickly and efficiently as possible.
I would imagine a later Volvo with a driver's side air-bag would be quite safe?