My 1966 Electra seems like it should ride alot smoother. It sure is a boat, but going over bumps rattles your bones. It's got the original shocks....do you think they're shot? When I bounce the car up and down, it is stiff. It doesn't just bottom out. It bounces maybe once more then stops.
Was this car parked for a long period and not on blocks? Could be spring fatigue from sitting on the same position plus the age of the car. I doubt the springs were changed to stiffer ones. Unless you have some heavy heavy duty shocks.