Those cars used different spec OEM front coil springs depending on the installed engine and options like air conditioning. So if you want a higher ride height you can get springs for a big block car with A/C.
New springs tend to settle a bit after a while.. For the rear you can replace the rear coils and add some Air Lift air bags. These rear air bags really help these cars with rear axle traction and extra cargo capability/ride height adjust ability.
Air Bag Suspension, Air Springs, Air Suspension Kits | Air Lift Company - Tow and Haul with Safety and Comfort
The suspension/control arm bushings are probabily shot too.