I use a K-N part # 33-2129. I cut the horizontal lip off all the way around. I cut the filter to fit the air box on the back, notch out and right hand side's leaving the original filter edge for the front and left side. Tin snips work well for cutting the filter. For front longer straight edge I epoxy'ed a 3/4" wide aluminum strip to the filter to help keep it straight. Cut the filter so there is approx 1/4" gap between the filter and air box lid. This gap is sealed by glueing 3/4" wide 1/2" low density (the soft squishy stuff) foam all the way around the filter. I found it easist to glue the foam in stages, doing two side's and set it in the lid to hold the foam in place while the epoxy cures. Then do the other sides. I used Dura-mix 40-40 to glue the foam, it's two part epoxy that comes in a twin tube applicator, and is resistant to fuel/oils.
Try not to make the filter to tight, as it will squeeze the pleats together and could reduce air flow.
Also the two "tit's that stick up though the foam will need to be cut of the lid.
To service the filter I just pull the 4 screws that hold the lid on, and leave the filter in the lid for cleaning/reoiling.