Component tweeters usually include enough parts for flush mounting and can also include some bits for a more extended surface mount.

Whatever you do however, do not place tweeters at ear level. They sholuld be relatively close to the mids if you want to preserve any type of functional/realistic sound-stage. Some auto-makers mount their component tweeters too high as well. This causes a much shorter path to the ear from the speakers on your side of the car and makes everything sound horrible.