Great post! My son and I have just started autox here in Central Florida. I noticed the event pics....The older mustangs were all in the class you should go for. CAM (Classic American Muscle) Very, very few restrictions and it keep you competing against other muscle cars not a bunch of miatas and stuff. Read up on the class....VERY VERY few restrictions. Engine, suspension or other. Basicly stay over 3000lbs and have an interior to fit 2. Nitrous bottle must be removed to compete...that's about it!
If you don't mind me asking, where in Central Florida? SCCA Auto-X? I am located in Central Florida as well and am looking for Auto-X events.
OP, if you don't care about classes, then just mod away. However, I suggest that you care about classes. The main reason is to try to keep the field competitive. Auto-X is a lot of fun, it's even more fun if you have a shot at being competitive in your class. Trust me. Knowing that you have a shot at wining (or at least doing well) vs. knowing you have no shot what-so-ever makes for two very different experiences. Both fun, for sure. But also both very different.
Don't do the brake kit yet. Start with the tires, and get the absolute best that you can. If you want them to be DOT-legal, then get the best sticky DOT-legal ones you can that you still don't mind driving on the street. If you are okay with a second set of wheels/tires, then get R-compounds up to your points allowance (if you are classed by points). Then get better brake pads. Then drive the car, see where you have issues, and then address from there. I think you'll find that starting with the tires and then working your way up the suspension (tires, then pads, bigger brakes if necessary, then bushings, shocks/springs, etc.) is a pretty good approach.
If you don't care about points and just want to have fun, then do whatever mods you feel like.