A-Body Autocross?

Take a look at the autocross events and providers in your area. Classes are very important, and before you start working on the car you'll want to decide which class you want to race in. If you're not an experienced autocrosser, it will be better to keep the car closer to stock. Which is fine, because there's absolutely no reason you can't handle well with the stock suspension design. Coil overs aren't inherently a better design at all.

Once you've looked at a rule book, set the car up. Probably something like this...

1.06- 1.12" torsion bars
Bilstien or Fox shocks
Front and rear sway bars (Hotchkis probably the best here)
Frame connectors (check the rules, "through the floor" connectors aren't allowed in all classes)
Rear springs for handling (120-130lb rates, low ride height)
Good alignment- negative camber, +3 or more caster, slight toe in
16" or bigger rims and sticky, modern compound tires. Check your rules for size limits though
Bigger brakes (check rules)
Stock lca's with offset bushings or tubular(rules again)

Autoxcuda and gmachineDartgt have their cars set up pretty well for this sort of thing. Theres lots of other things to consider, 16:1 steering, 4 or more speed transmissions, etc, but it's better to start small and improve your car as your driving improves, rather than build a bad *** car that has to compete in ridiculously fast classes against seasoned drivers.