that rpm boost is probably because the previous filter was clogged/the stock airbox sucks.
As far as the box goes.. look at will'* sig pic of his engine.. you see that box surrounding the cai? well that'* what you want. pay close attention to it, print out the picture, measure around the box, and go to your LHS [local hardware store, for hobbists this may be referred to as local hobby shop], and once you have all the measurements, a lot of the places are happy to cut the material for you, if you purchase the product from them. So.. what are you waiting for? hop to it!