Clutch etc lightening

This was posted on the old forum.
How could you do it? and what would you machine? looking at the clutch I cant see where you remove metal?
this was posted as an example of what was done on a guzzi <!-- m --><a class="postlink" href="http://www.guzzitech.com/Flywheelz-ed.html" onclick="window.open(this.href);return false;">http://www.guzzitech.com/Flywheelz-ed.html</a><!-- m -->
Ta
Ray