The only document needed to sell a car in most states is the title, I don't think Illinois has smog laws. Give him the certificate of title from the previous owner along with the permit and temporary papers, that should be fine, and if there are any issues, I'm sure they'll tell him what needs to be done at his city hall.
Also, in many states a car has to pass a safety inspection before it can be registered, but you can let the new owner worry about that.
