Gradl wrote on Mar 23^rd, 2014 at 9:55pm:

Thanks, I have another question. Is it possible to control the heading bug by the ISG Simavionics FMC or the CIVA INS ? I want to retrofit the 737 to use it on IVAO. Regards Gradl

Yes you can use the CIVA INS with the 737. Anyway the usual config used on most plane doesn't work with the 737 due to the CWS autopilot. It means that the CIVA INS gauge cannot control the heading bug.

Paul Tally made a gauge to make it work.
Check "Civa Ins Heading Display" on avsim

If I understood well how it works, it calculates the offset between your current heading and the heading needed to fly to your next waypoint. Then it banks the plane slowly to reduce this offset to zero....

I use this gauge, so I can tell you it works!