I would be cautious about using the stock shock mount positions to raise the car , via either air shocks or coilovers. The brackets up on the frame are not very strong! Shock ends sticking up through the trunk floor are not too uncommon in Chevelles of that era. If you just want the back up a little higher for now for the tires you want to use up, I'd look at spring spacers which are cheap and easily removed.
Do check the frame for cracking, where mentioned and also around the front spring cups and a-arm mounts...another common problem area.
If you really want the car to drive better and presumably have the stock SS sway bar set in there (if not then that's the first thing to do), common mods are taller front spindle "uprights" from other GM models (some of which use bigger brakes) and the a-arm mods or replacements to accommodate them, more front caster, stiffer shocks (BB cars need them, mine are from a Dodge truck), and a quicker steering-ratio box. The rr doesn't really need much if you already have the SS sway bar, control arms and frame bracing although stiffer links and bushings are available. Start by looking at Global West for suspension ideas and components, and if you don't like the prices note that stock a-arms can be modified by someone who knows what they're doing.
My big fat all-iron BB El Camino got the treatment (plus a little frame reinforcement) back when and it really woke it up. The basics are there, they just need a little tweaking.