Have HUD on all my cars, just speed, rpm, coolnat temp and bat voltage. Uses the diagnostic port for power and info.
Had a GTP as well and added the factory HUD and Navigation to it. I used the stock windscreen, not the "HUD" windscreen with no issues. What was nice about the Ponti was that it integrated the radio and navigation to the HUD (in addition to speed/turn signals/warning lights). The box was BIG though (you can adjust the angle of the mirror on the Ponti so that the image on the windshield is higher or lower). Electronically it would be fairly easy to integrate into the M but the mounting would be a nightmare if not impossible.
I mounted my current one on the M off to the side because the dash "pod" is in the way and I did not want to cut into anything. I use it regularly, in fact, I rarely look down at the speedo on any of the cars. I did put some very light tint on the windscreen to help with viewing during bright outdoor times but for the most part it the tint was not needed.