Outfitting my Iron Knuckles DC-9 with GPS

I just got the Iron Knuckles DC-9 package from Flight1 and am "upgrading" the panel so it is more realistic. I'm refitting two gauges so that it is more like a DC-9 cockpit you'd find today and not in 1960. I have already added Lee Hetherington's TCAS to the panel replacing the old VSI unit, now I need some kind of navigation tool.What do you guys recommend putting in? I'd like to replace the default FS9 GPS which is currently in the panel with something else. I have tried the ACS-GPS but don't really like the gauge since it will not operate if you hide the GPS gauge itself. I originally put the GPS in its own "window" so I could hide it when not needed. I suppose I could squeeze it on the main panel somewhere if it's the only option though. Also the ACS-GPS does not slave to the HSI, but rather merely commands navigation by use of adjustment of the "heading" function of the A/P. I would prefer that it gets slaved to the HSI so I can also manually fly the course using the HSI.I also considered the CIVA INS which I installed on my SGA DC-10. Is putting an INS on a DC-9 realistic? The CIVA INS also does not slave to the HSI.So basically I'm looking for some kind of navigation gauge which can accept a flight plan (like I am assuming modern-day operators of the DC-9 have) and also can be slaved to the HSI. I know it sounds like a lot, just wondering if it is possible? Or best yet would be to have some kind of basic FMC unit that I could install- I think Northwest Airlines has a simple FMC built in to their DC-9's.Anyways just looking around for some options. I will consider freeware gauges or payware gauges (if they are good). Thanks!Hope this was the right forum to post this?Ruahrc