Brad... Matt's further details are on-spot. In my opinion, with your car's setup, you'd be in the SM category.. a very tough class to be autocross competitive in... or certainly in C/Prepared... an all-out race class. Some clubs around the country have their own alternate sets of "regional" classes, etc. Rule books can be very difficult to follow, as well as interpret.

As a simplest and most pleasing option, you may want to re-consider and find road course events that allow you to open and use the full awesome power of your car for lapping sessions... could be "competitive" events, or else just "social" fun events.. and eventually lead into competitive events/clubs.

Seek the internet and get to know others in your area who participate... look at your reasonably close road tracks to see if they have clubs/organizations that hold events on their tracks... a typical road course lapping day is ~$200 (+/- $50) in US dollars (some events are 2-days at about $350 US dollars)... and you'll get about 4-5-6 20-30 minute lapping sessions per day.. a blast!... and those ~200 tw tires are ideal choice (per likely rules, if applicable) and will work great for that type of event.. tires should last 1-2, maybe 3 years at most if you're lucky.

Wherever you end up, I'll bet you'll have one of the most popular cars there!!!