There are two types of diamond bits for the dremels. Both should work equally well but for different cuts. One is a diamond wheel which works great for long straight cuts and the other is a diamond coated rotary bit for neat yet tight and curvy cuts.
I would take your old fairing and tape some heavy paper over the light and opening, then trace out the profile and get some measurements [if at all possible] as the the placement of the paper placement on the orgininal. Then transfer this paper to the new unit and make the first cut inside the profile by whatever you feel comfortable w/ [1/4 at the least I'd think..] rough trim to this line and then with lots of patience and test fitting, work outward w/ the opening until it fits.. there's no short fast way to do it unless you have some automated multi axis robot [which is unlikely ] Measure 1000 times if you have to, 'cause you only get to cut once.. any fool can cut it twice and the hole will still be too big.. it takes patience to get it right w/out messing up the part
Are you going to need some form of a light 'well' or something in behind the fairing to mount the light? or does it mount to the frame?
Good luck!
JerryFlyGuy
The more I know... the more I realize I don't
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)