Originally posted by bnoon:
You can fit a 9" in there with a regular mouth filter and a flangless Pro-M. 
...or you can fit a 8.5" filter (plus 1 3/4" flange) in there will some effort and shortening pieces...
The Filter is an RF-1027 Listed as 8" but that's only it's effective filter area. It's nearly 9" plus the flange.
It's not a direct bolt on. (Had to open up the MAF adapter to ~80mm and add a rubber boot around it) The good thing about it is now it's finally as large as the Pro-M's inlet.
