how tall air cleaners

How tall of a K&N type air cleaner will fit in a Speedster using Weber IDF's?

I understand that Dells are taller - if so how much and what size of filter?

Not your answer, but a helpful reference. I bookmarked this site after having read a related post by, I recall, Larry Jowdy. (?)
http://www.knfilters.com/Racing/customcarb.htm

I think mine are 3 1/2" and just clear the body.

I'm using 3 inch air cleaners on top of a home built 1/2 inch riser (Weber 44s). My reason for adding height was to install velocity stacks and still maintain 1 1/2 inches that Weber reccommends for clearance between top of velocity stack and bottom of air cleaner top cover. This was only possible by cutting a bit of the deck lid inner cover away. There is an inch of unused airspace between the inner deck lid and the outer deck lid. If you look carefully in the "hinges" picture, you can see the right side cutout. The left side fits just fine due to the set back (set front?). Additionally, I filed just a tiny bit off the corner of the air cleaner top cover to stop it rattling against the outer deck lid. No worries now. Obviously I don't care about authenticity, you may have different concerns.