Hopefully you brought the flash unit with you! This is a SUPER easy task!
Pavel is correct - and an awesome source of info!
I just did the same upgrade - also purchased the UWTechnics unit from Bluewater.
Of note, the hex bolts were under the mirror (it seems more like a mirror than a prism). You can almost see them if you lift the front half of the housing and try to look at the bottom/ under the mirror. My mirror was barely glued on in my NA-D800 housing. The mirror even moved when I placed the hex wrench into the left side hex-head that holds the base/ podium.
My greatest difficulty was actually the initial loosening of the original pair of bolts (2.5mm hex wrench).
Installed and ready to test tomorrow!
(Thanks again Pavel for all of your assistance and patient messages!)