Installed the second mirror mount to get this started because it appeared to be a direct drop in replacement.
The mounting plate goes over the motor, around the pulley, with a section milled out for the belt to pass over. This means you have to loosen the x-belt and remove it from the motor pulley. If you haven’t worked with the x-belt, the belt tensioning screws are on the right side. You access the screws from a hole in the wall between the laser compartment and the LPS compartment. Loosen both screws, shown circled, about the same amount until you can remove the belt from the motor pulley.
Mounted the new mirror mount using 4 M3 x 15mm stainless steel hex cap screws with washers and reinstalled the belt. Be sure not to over tighten the belt which can cause binding.
Lightly tightened the new mounting screws just enough so I could still move the mount side to side. Placed a piece of tape over the alignment wing and moved the mount back and forth, with test fires, until I got it centered on the beam. Tried to keep the back edge of the mounting plate parallel to the edge of the motor. Tightened all screws.
Aligning the mirror to the laser head actually went fairly quickly. Looks so purty
Got some PETG in for my 3d printer so as soon as I get that dialed in for printing I can get my adjustable tube brackets printed.