Your seat belts should have tags with date codes. You can check your dates and see if they all correspond with the date of your car. I previously owned late built 1972 Camaro with an 03D build date. It came with the newer style seat belts, where the shoulder strap attached to lap belt and had the shoulder strap pocket along the headliner. It still had the complete original interior when I owned it 10-15 years ago... I've posted pics here somewhere before. I'll see what pics I can find and add some here. I have them on another computer.