If you're running 140+ treadwear tires, (which it sounds like you are) then we only want to see the A (for AWD street tire class) on the side of your car with a number. You'll use DS (for D-Stock) for your index when you register. That's assuming an 08 WRX, if it's an STI then you'd use AS for A-Stock.
If you're a annual member you can go here to reserve a number, (46 is currently open). If you're not yet a member, go here to sign up. A lot of this is explained here.
I'd email John at K&M telling him you want him to bring two of the following, (one for each side of the car). 4, 6, A. If you ever plan on going to DOT R tires like the Hoosier A6 then have him also bring a couple D's and S's. He's got white and black but may have other colors available. Remember to use contrasting colors, black and red or white and silver are usually bad combos.
Let us know if you have any other questions.
Thanks,
Jeff