Here are some measurements of the panel I installed in my LNC2.

First of all the face of the lefthand panel is 27.25" from the after side of
the firewall.

The forward face of the panel immediately above the radiostack is at 28.75".
The top tray is less than0.5" below the top of the radio stack fibre glass
moulding.

I have a vertical card compass mounted on top of the panel immediately above
the radio stack.  This compass is 3.5' high and clears the inside of the
canopy by 0.75"

The audio panel tray is the first tray in the stack and is 1.5" below the
canopy, at its forward point. This tray as you can see from the photos is
much shorter than the GPS/COM immediately below it which clears the canopy
by 0.75".  I can see that you could have a problem in this position if the
tray was as long as the GPS below it.

If your AI is in the same place as mine, standard 6 pack configuration,
then it must be much longer than mine which is approx 6" long and clears the
canopy  by 3".

If any of this helps, fine.  If not, feel free to ask any question that
would help you and I will do my best to answer.

Oh by the way, I am 6'-2" or thereabouts and getting my knees under the
panel is possible but I would not want to have it any lower or further aft.
I seem to remember that I hot glued the panel in place to give me a feel as
to how far aft I could go and how low.

Regards

Ian Crowe
C-FKRO
Taxi tests start this weekend.  C of A awaited from our equivalent of FAA.
Final inspection was a breeze.  Watch this space.