Sorry, but in my opinion, air shocks have no place on a performance car. One main problem is that if they are used to allow the use of wider tires, if the air line fails, the car becomes undriveable. I once had air shocks on a Dart because the wheels I used stuck outside the wheelwell. Hey, I was 17 at the time and thought it looked cool. The air line rested against the exhaust and the car sunk down atop the tires. I had to get 2 spare tires to drive the car home.
Replacing individual leafs would work, but you will need to be careful there too. The main leaf in most A bodies isn't very thick. The second leaf only extends to within 7-8 inches from the shackle. If you use stiff truck springs in your spring pack, try to use a leaf that extends further rearward to the shackle. The 7-8" of unsupported main leaf can and will bend if the rest of the spring section is too stiff. SOMEthing has to give.