I would not mess with the airbox unless your planning to remap it.
To do it right, you should install K&N, set of aftermarket canisters,and a power commander. Then you take it to a knowlageable touner and have him toune it on a dyno. During dyno touneing he will decide if more holes are needed for biger air flow in the box. With this you should get about 100hp at back wheel and a very responsive and crisp throttle and most important a considerable gain in botom and midrange :lol: .
One of the nicest things you can do to this bike is add 2 toth biger rear sprocket.