I recently did some work to my (admittedly different engine - 2002 Black top Zetec) but I used a K&N filter in standard airbox and redirected the intake to cold air under the car using Silicone Ducting as other suggestion.
I listed this on my Le Mans 62 website with a download on the process at this
address and may give you some ideas. I must say it has certainly made a significant difference to my car.
