I noticed that the primary has a plate attached to the backside of the clutch. what is it for

Think of it as a vibration dampner

In theory , supposed to help in harmonic sound or vibrations

Cat started it as part of the sound reduction kits or recall on the 2003 F5 and 2003 F7 as they initially didnt leave the factory with them installed

Included the rings - Different Hood padding - Foam by the clutches etc.

Then in 2004 all this stuff went into production sleds

Like mentoned above it was for sound......my brother has an 03 F7 with out this update, he went to the local dealer to inquire, found out what it was for but the dealer said that the update has expired and if you wanted it done he would have to pay......I realy do think that it makes much of a difference, I ride with two people who have 03's,one has the update and the other one does not and I can not hear or see a difference.

07s dont have em, at least the 800 XF doesnt, has a very thick fixed sheave (1/2" thick or so)