Mike
I just did a quick review of the SCCA Solo rule book. Initially I thought you would fit in STS. But I believe that the springs and throttle body are mods not approved for STS. So that leaves Street Mod. I may be way off base on this, so don't hold me to this.
When you initially start autocrossing, the local SCCA group, Central Florida Region, has a novice class. You could start out in that class, and conpare your times with the class you car would normally compete in.
I would suggest that you look for Danny Shields at the autocrosses. Danny is a several time national champion, and is eager to share his knowledge of the sport. In addition, he has competed in Neons for several years. Danny drove a Porsche 944S last week at the Tampa fairgrounds. When Danny is not driving the 944 you can find him in a Boxster. His car number is usually #5.
I like to suggest to drivers who are just starting out in the sport to forget comparing your times with other drivers times for the first several events they drive in. I feel the most important thing to focus on is improving your own times on each run. By focusing on improving your own times, everything else will fall into place.
I look forward to seeing you at the events.
Dave