You can enable both sorts of navigation equipment in the CS 727.
You already can see the default GPS there and there's a mod around where you get some "Nav" switch on the AP to follow it. This would be the easiest but less authentic method though.

The Civa INS can be integrated too and fits much better to the character of the plane in my eyes. Some guys even fly both mods, so they can switch or check their stuff while the basic 727 installation just goes VOR to VOR or by setting the heading bug to "home" and watch the fuel flow.  ;D

All mentioned mods can be found in this very forum section. They are free and just need a text editor as a tool to work with.