Hi Jacob,
Lipo is allowed, just make sure it is a BRCA legal Lipo as they are tested to ensure they are safe. (check here....
http://www.brca.org/BRCA/elecboard/n...%20List%20.pdf)
There are no classes for different motors, it is all modified so you can run any motor including those you listed. The only seperation is between 2wd, 4wd and trucks (if there are enough).
Nigel Buck is running the Durango and will be there regularly. There are also a couple of Durango team drivers who race occaisionally depending on what other races are on the same day.
Let me know if you have any more questions and hope to see you soon.