--best of show (overall best car period)
--best paint (1st, 2nd 3rd)
--best engine (1st, 2nd 3rd)
--long distance (1st) Makes guy who went out of his way happy and will return with friends
--peoples choice (1st)
--best original/unrestored (1st, 2nd 3rd)
--best hot rod (1st, 2nd 3rd)
--best under construction (for teh same reason as distance award)
--best GM, Mope Ford, Other (1st, 2nd, 3rd, 4th in each, then all #1s go against each other and best car of the 4 is best of show-others go to 1-2-3 and 4th in wining group becomes 3rd). Best to have you other car buddies who know other brands judge
With these kind of categories you can get it done without being an expert in all brands, nothing is worse then a Moapr guy trying to determine if the bumper on a Talledega did in fact come from a Ferd station wagon (this is true). Living in Motor City will be tough though
You can go nuts with categories depending on turnout and # of trophies you want to give out:
Street Machines
Vettes
Antiques
Low-Riders
Late Model Muscle
Dare I say it, Foreign
Hope this helps Good luck!