Figured I would post this here to make it easily searchable to someone brave enough to open these in the future. It was very difficult for me to find this info when I was looking to do it so happy to provide the info to help others.
Also happy to answer any questions regarding opening the headlights but be warned, it is messy and time consuming. Which I guess is why you don't see many doing it.
Here you can see the "light-pipe" design of the OE rings. This is the reason changing bulbs results in very little improvement in brightness and only a color improvement no matter how bright a replacement bulb you install.
Inner (larger) rings: ~5 11/16" (144.4625mm) side to side and ~5 7/16" (138.1125mm) top to bottom
Outer (smaller) rings: ~4 7/8" (123.825mm) side to side and about exactly the same top to bottom
