A-Body Autocross?

Boglin, If you find a local organization with no classes, no restrictions, and you're having fun, then go for it. You might look for 'track days' and things like that.

72bluNblu is giving you good advice. I like Bill Reilly and I like his products, but that's only one of several routes. It has the disadvantage of placing your car in a very prepared class, usually very competitve. In SCCA, it would at least put the car in C Prepared and that means serious slicks and tuning time. You can look at the Sandberg's AAR as the for an example of a fully developed CP Mopar.

There's a link on my website to a couple of guys in Canada who were autocrossing their 'cuda on your side of the border. Not sure if their webpage is still up - its been a while since I've checked.

My only additions to what 72bluNblu wrote are:
Build your chassis tune around the tires. Change them and it has a major effect.
Competition R and A compund tires are available in 15", 16" to a lesser extent unless you're look at stockers, and 17" is probably the best selection unless you're looking at slicks. Your choice will depend on the rules, weight and ride ht considerations, and whether you will have to use them on the street.
Make the car lighter!
Slaloms require faster ratio steering 16:1 power or manual is very helpful.
Rear sway bar should come last, and be light.
Shocks are very important in autocross. Koni's and Penskes if you get real serious. Whatever you choose, remember if you've lowered the car, make sure the shock doesn't bottom out.

Another route is to go toward rally motorsports. Stock based suspensions do very well with only a bit of tweaking. Of course full closed course stage rally is a high risk game. Expect serious damage as part of the game.