The assorted classes are run differently as far as index, dial-in, headsup, full or pro tree, etc. ATCO is running a National Open the first weekend of May. I don't know if they will run Juniors, but they will have all of the normal big car classes. That may be a good place to go and get a feel for what all of the classes consist of. Get a copy of the NHRA rulebook. That's the best source for the nuts and bolts of the different classes.