Just a quick link to the gallery for now. Basically I measured the center of the mirror and holder and stuck on some 100% silicone adhesive.
Post questions in the comments!
A good workspace
back of mirror
measure both axis to find the center of mirror and align to center of holder for axial alignment of the tube to mirrors
some whiteboard math
draw and measure the calulcations and leave airgap using some toothpick spacers (removed later)