I know that right now you are shopping for sun visors,
but did you ever consider shopping for shoulder belts?
It saves a bundle on sun visors - plus your rescuers don't have such a
mess to clean up! - Hopefully

I have 4 point inertial shoulder harnesses that I had installed 6 years
ago. They were almost $2000. They seem to work to arrest forward
motion sudden stop, but don't stop vertical motion. Seems like an
old-fashioned lap belt would work.