That's crazy! It is working fine, and I am not th only one that did this. I got the whole AFAM aloy kit, and along with the 520 chain, took off alomost 7lbs!
Try Motowheels or here:
Ducati 520/525 14/15T Drilled Front Sprocket
520 conversion dropped 7lbs??? Really? Typically a 2lb weight savings. Maybe a nudge more with aluminum sprockets.