The block off plate just gets screwed down with the self-tapping screws. Yes, that means putting a couple holes into the body of the vehicle. You could try something like commercial grade Velcro, but with all of the heat, I have no idea what would happen. Could turn to goo and just be a mess.
As for the 9" filter, I've been told that one will fit, but my personal experience with this install would say that it would take a bit of work to get it in there. The fender well isn't a huge space to put one in, but like I said, I was told that one would fit.
