You are correct. Those are spring 'helpers' that were used to add some height to sagging stock springs. Back in the day new springs were pretty pricey so those 'helpers' were a cheap alternative. I used them myself on my 1968 hardtop. I am surprised a set survived this long. They are still available in various forms. Another item commonly used was the little aluminum, 'knuckles' that you twisted into the front coil springs to get some height back. Band aids for sure but they worked.