The only thing I can say about this is that FSX is buggy. We had a discussion on VOR navigation  and how the track of a particular VOR was off by quite a bit.  The ATC was informing us that we were off track and to "turn to heading XXX" to get back on track. This was confusing as the VOR track was wrong compared to both the GPS and ATC, but according to the HSI, we were tracking the VOR correctly, although we were really 3 or so miles to the left of the Flight Plan displayed on the FS GPS. This was happening in the Captain Sim (727, I think) aircraft as well as the default MSFS aircraft, so I/we concluded that it must be FSX causing the fault, not the Captain Sim aircraft.

As for the rest of your query, this reply from LOU in the 727 forum, might help you with how it is done: http://www.captainsim.org/yabb2/YaBB.pl?num=1299896115/29#29
If not, hopefuly he will jump in here and help you out.

Mark