Bad idea mate (with the greatest respect).
The whole idea of an airbox is that it is a sealed air induction system that provides consistent performance (usually by keeping the air temperature within a certain parameter).
If you drill the airbox, it will remove the aforementioned benefits and may reduce the performance of your car in a number of situations, especially if the effect is to give the throttle body unfiltered air.
Most Mk1 16v/Williams drivers are well aware that using an induction kit makes for a reduction in performance because of the hot air that gets sucked in - and I doubt its much different on a Mk2 1.6.
By all means use an IK, but youll soon want to keep the old airbox handy for the summer months and for town driving. So dont drill the airbox! It isnt a free and easy power improver!