articles types are not associated with permissions. Instead, topics are. So, you should be able to achieve what you want using both a type and a topic (if you really need a custom type).
I'm not an articles user, but I would be surprised if there was a way to get different permissions on article body and header without a bit of hacking.
One way to work could be to publish articles and put classified content in a Wiki page each time. There are currently no email notifications for articles, but there are for Wiki pages updates.