Originally Posted by fastnoypi
only difference in the kits are the idler pulley to fit the bolt length that came on the stock idler pulley. You can get either kit, and get a new bolt from the dealer if the idler supplied is wider. IIRC, the 04+ idler pulley bolt is a few mm longer than the 02-03 bolt.
FWIW I matched everything as 04 STi since the parts design superceded anything designed during the 02-03 years.
Yup, most of the timing components for the 02-03 has been superceded by newer model year parts. Here is the picture of the original EJ207 pulley that came with the motor. As you can see, the mounting face is more recessed inside the pulley. The new idlers will have the mounting face closer to the outer edge of the pulley, thus necessitating longer bolts. Sorry, I didn't take a picture of the new idler before I replaced it. I'll try to find time to unbolt the timing belt cover and snap a pic for you.