I watched a fellow around 1967 remove several hail dents with dry ice in a relatively new Nova...body shop at a dealership. He parked the car in full midday sun for a couple of hours then broke his dry ice into pieces about the size of grapes. He then put a piece of dry ice into each dent and within a few seconds most of them popped out. He said sometimes it took a couple of tries, but added he could get all but the really large ones out that way.
