There is confusion about the two PC-6 models I believe.
In BAT, we have both.
PC-6 air.PC6ED 1 NOINFO usa01 SUMMER
This is the Edlor model (ED for Edlor...). It is the one without mirrors - but also without collisions, damage and generally unfinished.
At one point I unified the cockpits and made its cockpit reference the same 3do folder as the avaiskins PC-6: PORTER. Now with you modifying a cockpit fitting on the aviaskins 3d models, and also use the PORTER 3do folder, you mess up the PC6ED cockpit.
The screenshots form snd-73 are showing the Edlor Porter, which will apparently become its own thing at some point.
There's a simple solution to the cockpit issue though for the time being.
Rename your 3do/cockpit folder PORTER2 and make the CockpitPORTER class direct to that folder. Then both models have independent cockpit 3do folders.
This is how I will integrate this into my BAT and consequently into a future update.