Air bags and air shocks will significantly degrade your ride quality. Air shocks are worse because they support the vehicle on the shock mounts that are not designed to carry much of a load. I am not sure why you would want to raise the car that much. If it is for tire clearance then it would be better to use a wheel with the proper back spacing. I have a 65 LeMans and I use a Centerline wheel with a 5 inch back space that seems to put the wheel right in the middle. I recommend Springs and Things (
http://www.espo.com/)for purchasing springs. They also offer a spring for your application that will provide a ride height one inch higher than stock. I don't recommend going any higher than that. If you must raise the car it is better and safer to raise the car with a taller spring or by shiming the bottom of the spring perch with an aluminum or hardwood shim. Yes hardwood works fine.
Tim C
65 LeMans, 3600lb. all steel, full interior, D-ports and a flat tappet cam, 11.01@120