You need to read the rules for the various classes. I'm not sure you would be legal in autocross without doors. Certainly not in any of the Stock, Prepared, Touring or similar classes. No offense intended, but there are safety issues, and you can't just run any old piece of junk.
Safety issue is one thing, but another issue is weight advantage. Doors are heavy, you would have an unfair advantage in regular classes if you pulled the doors.
You would be better off pulling the dents out the best you can, and welding the doors shut if necessary.