I would use Merritt Carden in the Bay Area.
At Centerline we recently had many sets of gears lightened for the 105/115 cars, and our very experienced machinist (he has parts currently on Mars) did botch a few gears before he got set up to do them perfectly. Obviously, if you are only having two sets done munching a gear is not a good option, so experience counts.
If anyone is looking for 105/115 gears, we have these on the shelf, ready to ship:
http://www.centerlinealfa.com/new/lightened_gears.html
Joe