Excellent advice Les
and, yes, the bracket is an excellent piece of kit - well made, precise, and a very good price in to the bargain.
If any others with a 1200 GS or Adv want a way to mount HID ballasts, I would 100% recommend Les' bracket. I have 2 ballasts mounted behind the side panels using a costom bracket from the USofA (can't remember the supplier), but Les' bracket is way easier, and it dopesn't need modifying - I just 'rounded' the edges where it has been laser cut.
100% recommended if you're going the HID route ( which you should! with Colebatch's 50W HID's!)