Helper springs will work, but you'll be able to see them from behind. Not sure if that's something that would bother you or not.
Air shocks work. They were an accessory option on all Pontiacs. They don't require additional strengthening of the shock plates or upper mounting points. They have a rougher ride than regular shocks.
Because I change wheels often, going from same-size Rally II's to a set of redlines with Rally II's, and also a set of slicks with smaller pizza cutter tires up front, I run air shocks so I can keep the car level.
New springs are the way to go. But because of the one-size-fits-all replacement springs out there, you run the risk of getting springs that will have your car sitting 3 inches too high in back.
But yes, new springs are the ultimate solution. Getting the correct ride height (and stance) is the tough part.
