Probably not.
However, I think the primary benefit of seat belts in antique cars like this is that they keep you positioned in front of the steering wheel. During evasive maneuvers, skids, spins, etc, vinyl bench seats don't do a good job of keeping you in place. Even during normal driving situations, making turns or going around bends, the belts keep you in place and prevent you from possibly losing control of the vehicle.
With vinyl bench seats it's very easy to slide out of position during quick maneuvers or during an emergency. Staying put behind the wheel - even with lap belts only - is an enormous benefit whether or not they prevent you from hitting the wheel or windshield in a high speed crash.
Exactly why I added lap belts. Many years ago when I was young and stupid(er) I slid across the seat taking turns too fast. Put a healthy scare in me.
