I currently have air shocks on my 1966 chevelle, came that way when i bought it, would air bags in the coil springs be any advantage , ride better easier to level car, currently have to run 100 psi in pass. side 50 psi in drivers to get rear end level [28"] if i go air bags i would have to trash the air shocks and put reg. shocks on ,right .So i guess is it worth spending 200 bucks[Canadian] for bags and new shocks also running 15" 275 tires so i do need a little lift

Rocker,
Sounds like you might want/need to dive into that rear suspension and R&R it. Rear springs can be purchased pretty inexpensively from Moog or TRW and I do believe bushings can be had for about $100. Get a good set of shocks and be done with it.

I'm sure others will chime in, but IMO you might want to look into some suspension work.

Joe