I went on to K & N website and ordered directly from them. I measured my stock carb where it bolts on, and it was about 67mm, and my buddies aftermarket carb, which was 63 (I want this one eventually). So I looked on the website under universal filters, and went for the round straight instead of the cone because it fits better with the prefilter. The inside diameters (where it bolts on), k&n offers 62, 64, 65, & 67mm.
I got the 65, and I had to tighten the clamp down alot.
In hindsight, I would have gotten 62 or 64.
They are more forgiving than they claim.
Make sure you take an accurate measurement, and also measure to see what length of filter you can have without hitting your shock or something else.
The filter, prefilter, + shipping was about $55 from K&N's online store.
Here is a pic:
