can i make a few suggestions here,
although drilling the airbox is great for noise it really doesnt give much extra performance. due to the heat in the engine bay all you are doing is drawing hot air in. if your only after a nice grunt then fair play.
performance panel filter with a cold air feed is the way forward. its pretty straight forward to rig up. ive done various testing on this and the heat generated within the bay is incredible. also smoothing out the air box and removing sharp edges will make a difference, seen a few mods in the past where a home made heat sheild is used to protect the airbox to.
dont get me wrong i previously drove round for a year with a drilled airbox but now im after more horses solooking for all the gains i can get!