you dont have to register to just go hangout pre registration from what i understand is to make sure you have a spot so you can be judged if you dont pre register your running the risk of not being able to enter
I can't see them putting an 04 in a classic class. I think since it's all Mustangs they should be a lot of classes making it fair. I went to 1 show that had 1 class for ALL modified cars from 1955-2000 that was a little uneven lol