Gary, Bob, et al,
I have mounted a vertical card compass on the forward end of the overhead
air plenum.  The universal overhead mount p/n PACMO-U from AC Spruce can be
bent to fit the plemun's forward face and support the compass nicely.  I
used NutSerts in the plenum to accept #6-32 screws.
The compass mount uses a foam rubber vibration absorber and its sticky glue
will lose its two sided stick in the heat of the cabin/windshield upper
area.  To insure the compass's azimuth does not change after the glue "dies"
one must fabricate rails on either side of the support to keep it pointed
ahead when this failure occurs.  Small bits of extruded angle attached on
either side will prevent rotation when this takes place.  I was warned of
this by a friend who supervises an avionics shop.  It's one of those "old
indian tricks".
Lighting is easy as wires must run to the overhead for the door seal pump,
etc.
This is my best effort at mounting a compass in the IV-P other than in the
panel itself.  It is as far as I can place it from magnetic and electrical
interference and still have a reasonable view.  One may need to lean back to
read it well depending on one's eye accommodation.
Walter Dodson    IV-P  N990Y  86%?