Steve,
Well done and well documented! I have done a similar conversion on my BT7 Tri-Carb, but differs from your project as follows:
1). I used LED lights instead of halogen bulbs. The LED's were purchased from a company called Harrison Specialties on e-bay. They now show up on Amazon when searched.
2). Used a couple of store-bought (from the local "Mom & Pop" hardware) washers of differing sizes to sandwich the LED lights. Holes were drilled in washers, and secured to shroud by screw-head bolts, nuts, and washers.
3). I used the earlier style conical lens assembly, as it looks more like a tail light than does the later reflector assembly.
Conversion/upgrade was done at least a couple of years ago.
Jerry