After all the issues I've had with this setup (no fault to pclear -- he lucked out), as have a few others with the shorty, I really recommend leaving the stock airbox IN PLACE. Remove the snorkle if you want the s/c scream, but the airbox should stay. I don't think it'd be too hard to fit the 3" cone filter in there.
It will act as a heat shield and also allow the filter to suck up non-disturbed air, when the radiator fans are on.
Worked okay when the temps were cool, but for the last month, I've been dealing with daily CELs and limp mode. Ended up buying the K&N CAI.
Moral of the story -- leave the stock airbox in place, rig up a cone filter per instructions above, and take out the snorkle (from the airbox to wheel well) if you want the s/c scream.
2004 ION Red Line
13.6 @ 105
13.7 @ 107
2008 Astra XR 3 door 5 spd
31 mpg, mostly city