I used a K&N 1250 and just put it on the carb at first. I read somewhere that having a longer straight intake track was a good thing, (don't ask me how. I've slept since then and thus don't remember) so I decided to modify the rubber intake track to the airbox to work with my K&N. I shaved down the inner diameter on the filter side of the rubber track, and my K&N actually fits INTO the track. It looks like this:
For the airbox, I chopped it up because I wanted to keep my side covers. The left side of my box is just a mounting bracket for my black box and solenoid:
The right side is an unfinished storage box. My plan is to use fiberglass to complete the shape and use the box to store tools. I'll have a screwdriver taped under my seat to take off the cover, though I normally have my Leatherman on me anyways.
It's unfinished, but it looks like this:
All closed up, it looks like this (minus the sissy bar that I traded for a stock one):
***EDIT***
One thing I DON'T have pictured is the inside of my K&N. I had to support the inside in order to mount it into the rubber I took a large hose clamp and I cut the gear screw off so that it was just a big metal band. Then I put it inside the rubber throat of the filter so that it pressed against the rubber track clamping down on it. Without this, it just tries to fall off.