Well done with the upgrade! I still need to get around to upgrade all mine. I just need someone to build me a sub enclosure that tucks away in the back passenger side of the trunk (I know someone on here built one that looks pretty money)! But I just got some pretty nice stuff that my insurance company got me to replace the equipment that was in my Jeep (Yes, after 7 years of intrusion-free fun in my Wrangler, someone finally cut my window and broke into it and ripped out all my stuff--serves me right for having all that in there, I suppose).

But to return to the current topic, I also had centering issues with my Z1. When you remove the factory head unit, the bracket that mounts to the vehicle itself fits snug around the head unit, and the bottom of the head unit rests nicely on the bottom of the bracket. So when I installed the bracket on the Z1, I used the bottom as a "reference point" and installed the bracket with the bottom of the head unit resting on the bottom of the bracket, just like the factory head unit was. When I installed it, I noticed it wasn't centered vertically, so I repositioned the unit so there was a bigger gap between the head unit and the bottom of the bracket. The screws didn't fit quite as naturally (i.e., they didn't go in as smoothly), but they did fit all the same. Once I reinstalled, I was much happier with the positioning (as you can see by the pictures).

So give it a go, and see how it works out for ya. Good luck!