I've been told by people who've tried it that it doesn't fit. IIRC they made a diffuser with a wider opening for the 323ti, however even that cutout is too small for most mufflers. Clex2 did a nice writeup on plastic welding as he cut his diffuser on his 330ti ClubSport. This is what I plan on doing:
http://www.318ti.org/forum/showthread.php?t=10544