In the 707, all I did was:

1. Install the freeware CIVA INS
2. Backed up the original panel.cfg by renaming it panel_bak.cfg
3. Renamed the CIVA_panel.cfg to panel.cfg
4. *CUT this line: gauge04=../civa/INS!Config,         0,    0,  0, 0, csx701 (from [Window00]) and
   pasted it in [VCockpit01] as gauge27=../civa/INS!Config,         0,    0,  0, 0, csx701
5. Saved panel.cfg.

It works fine.

I did do a dual INS panel a long time ago, but I prefer to use a single unit (i.e. the CIVA_panel.cfg).

* Doing this means that the CIVA INS is initialised as soon as you load the 707 into FSX, rather than having to press SHIFT+1 to initialise it.