Use plenty of tape up top and air cut to make certain. Offset to .01 until the last pass to keep it smooth.
Optional:
Use an offset to get the holes slightly larger than 1/2" in helix mode, then switch to a straight cut 1/2" bit and helix it out to final dimensions. Worked well.
For the mounting holes do the smaller first... may want to offset the holes a bit for alignment. The larger, cut to a depth of 13mm.