How do we know the 64E's are the Fanblades, and the 64W's are the Bullit wheels? I don't see anything in the 06 order guide that says this.

Well, we've seen the fanblades on the show cars. As far as the Bullitts go...no one knows. It's assumed the fanblades wouldn't have late availability, so, subsequently, it's assumed the Bullitts will be available late, as such stipulated in the order guide.