Keep the original airbox and fit an induction kit into it then remove the resonator and fit the intake pipe from a GTA (search the forum for GTA mod). The reason for keeping the original box is to drastically reduce the risk of hydrolocking the engine. You're also best to use a non-oiled filter as the oiled ones can kill your MAF. Many of us have used the Apiro Torque universal filter from Regal Motorsport, it costs peanuts and really does work.I would rather get rid of the stock casing and have a cone tbh, so I agree with you. I think that's the way I'll go, but I would have preferred a blanking plate to ensure cool air.
There's a great thread about it in this lounge, I'll dig it out and post the link...