Air shocks suck. If you replaced the previous springs with correct new springs and don't like the ride height, then you need to have a different spring.
This company will build you any spring you want:
http://www.coilsprings.com/
Back in '95, I had just finished the 3 year frame off on my '64 GTO convertible. I used the "correct" springs from our vendor for the front and the rear. What I learned was that from the factory - these cars rode lower in the rear.
I ordered a set of springs and requested .75" over stock. That's exactly what I got.