I installed a set under some Ford Explorer mirrors. Most mirror mounted lighting is a PITA to install. You have to pull off the inside door panel, remove the mirror, mount the light, run the wiring, and then close everything back up... They're time intensive, but turn out very nicely
I would pull up some install instructions from Whelen on their mirrorbeams for impalas. There's the instructions to disassemble the door and mirror, then just run the Ghosts and reinstall. No point in reinventing the wheel...