Any autocrossers on here?

I think I made 6 events this year, maybe 7. Last event I shared someone elses car due to the condition of my car's axle splines.

Let's See Your A-Body AutoCrosser
ANY AUTOCROSS RACERS

Check the rules your local club is running. Most, but not all, are SCCA sanctioned and use SCCA National Rules with local supplements.
The coil over rear will probably put the car into C Prepared, but may be OK in CAM C. But do check. Even for CP there were restrictions on how the usspension was connected, otherwise it would get put in Modified. I haven't looked at those rules in years so just giving you a sense of the landscape.

In C P, there are (or were) wheel size restrictions. See what you can safely tuck in there before deciding. Partially used racing tires could be picked up off-season. Also see what other people are running in your region. If you're not going to National level events and no one in region is either, then you may find there is no need to go so extreme to be in the game. Years ago all the classic pony cars in NNJR ran in ESP or CP.

CAM C is another ball of wax. The CAM classes are restricted to usiung a 200 treadwear rated tire. Again, see what fits but for the most part you'll be looking in 17 or 18" rim diameters. My suggestion is to stay as small as you can with wheels to keep down weight and height. The 200 TW competition 'street tires' are not cheap so may be worth picking up a rim and used tire to do some on the car measuring and checking. Allow some room for tire and wheel flex.