how to pick a class to race in

I hope sometime this year to run the car a few times. I will be using racing slicks, automatic, prefer open headers but am being told classes require mufflers. So I was wondering, do different tracks have different classes or are all tracks the same. I havent raced since the early 80's when almost everyone running street cars ran a class called "heavy". I hope to run low 12's or high 11's. I dont think I will go lower than an 11.49 but I did install a 6 pt roll bar. I plan on aftermarket belts so I am waiting to purchase when I am closer to being ready. I have a drive shaft loop and fuel lines will be solid not rubber. Wheel studs are long with open end lug nuts. Valve stems are metal. so I was wondering what class do I run in and what else do I need to make sure is on the car so tech is no problem.
Rod