I've only heard bad things about doing that mod but I've never done it. one of the best airfilters is a motersavers but it wont fit very well so you will have to look up ho to mod the filter where it will fit better i like to use shoe goo to hold it.
If you really want to get more power than use the OS18TM header or move to a one piece pipe like a THSracing, Trinity power, CVEC.. you get the picture.
You lookin to get maxx power out of your mill go with the trinity. I swear by them now and will never go back. There loud but they make the power shine.