Jamie,
RE: The GPS, you can copy the default GPS from any default aircraft. Here is the one from the Baron. Just replace Window 2 in the panel.cfg with this or copy it from the Baron:
[Window02]
Background_color=8,8,8
size_mm=230,220
window_size_ratio=1.00
position=8
visible=0
ident=GPS_PANEL
gauge00=gps500x!gps, 0,0,230,220
The .air file is the primary issue here. I cleaned up the aircraft.cfg and replaced the .air file with the Baron's .air file. Seems to work just fine.
If you want to try mine, get it here:
http://www.flightsimonline.com/mas/TwinFM.zip