It was a couple of the little waterproof horns that I put on the Norton.
I weighed them yesterday and can confirm that they are 100g each. Interestingly the stainless bolt, nut and washers weigh in at 26g. I have used a few aluminium bolts on the Monster in low stress areas and they work fine for a fraction of the weight of stainless or Ti.
I also use aluminium nuts on them and sometimes nylon, which are never going to corrode.
The little horns and alloy brackets replace the original structure on the Commando, there was also another Altette the other side. not sure how much this lot weighs as my scales do not read in Solar masses! (It was held together with 12 5/16" bolts and nuts and another 4 to hold it on the frame!)
I've also replaced the two coils with a twin output one which is an unintentional weight saving, but something to think about on a Ducati if it would work? Don't know if you might even have 4 coils on a twin spark motor?
The new bracket is made from alloy channel and doubles as a heat sink.