The current (iPhone 12 & 13) have the MagSafe magnet ring on the back which gives the combination of power at up to 15w (USB C cig lighter and good cable) as well as the slap to attach mount. In the MB and Aero I have found these to be strong enough to hold so far. I have the iPhone 12 Max (big one) Pro which is about the heaviest in the apple transparent ploy case with the mag rings.
With the head unit I am probably similar to you, it is more about the volume control (for the co-pilot as much as me) and not looking totally out of it in the lovely dash I guess.
Everyone loves a Morgan. Even me, unless it's broken again.
I found a good video of the installation of a "floating" touchscreen with Apple/Android auto. Looking at the mount the display can be dropped quite low. The side view during install (14 mins)shows the top of the screen almost aligned with the top of the unit. Just in case it helps.
Everyone loves a Morgan. Even me, unless it's broken again.