I recommend not to destroy the airbox completely. Instead do what I did as shown on the picture HERE. Naturally you can do what ever you want but I'm happy with my mod.
Not bad noise but plenty of airflow ... The ass-dyno reports plenty of difference compared to original. Too bad, the dyno charts are not yet done. Current mods: airbox, PC III, 2-1 custom made exhaust. The new pipes are car coolant hose; no idea about the diameter.
Now I would measure the diameter and cut the airbox conservatively to tightly fit the hoses instead of aggressively cutting of the front end of the box.
Very best of regards:
MotoJussi - California Jackal
jussi.savola<at>intellitel.com