First off YES no 40, 50, or 60 year old car is going to be considered "Safe" by today's standards. Too many things have happened to automotive industry since any of these now "Old" cars were sold new.
Something that does seem forgotten here is the fact these "Old" cars have a lot more metal to them then your adverage run of the mill, reynolds wrap cars/trucks of today which are 90% PLASTIC!
Do we need more safety features on a plastic car? Well........ I'd have to vote "YES!"
(let's not even go to "these cars are dinosaurs. these land yaghts need to be scraped and none get as good as gas mileage as todays cars.") If you think I'm joking about this do your own comparison. A '57 Chevy is NOT as large as some of today's SUVs or duelly quad cab pickups. Do those get good gas mileage?
Okay back to the point. (now what was it?)
Seat belts in a Classic car.
You can buy new belts from several vendors these days and install them yourself. They do need mounted through the floor pan and some type of stiffening done at this spot like using a large flat washer on the underside of the floor pan.
I do know of a guy who put seats from a Cadillac in his '55 Chevy and they do have the shoulder belt incorporated in the seat. So no anchoring of the should belt is needed.
PS. sorry for hijacking the thread.