Practically guaranteed that the rear leaf springs are broken. Leaf breakage on F and X bodies is epidemic.Your suspension is already lower than the factory specified ride height by an inch and a half or two inches lower due to spring sag (that is front and rear). So all you need is a floor jack in the back to pick the rear up two inches and that is what your car would look like if you replaced your rear leaf springs with stock ride height springs.
Amen to that. Went short and stiff on my Nova, didn't care for it to much. Have tall and soft on the Chevelle and enjoy the ride much more. Still corners well too.Before you buy replacement springs, figure out if you want tall, soft springs, or short, firm springs. The car will be night-and-day different to drive even if it sits at the same ride height.