If they are on the ground doing a hospital transfer then its unlikely they will hang around for long enough for a look around, they will be heading back to base to refuel ready for the next call.
If they are exercising with the MRT or something then its more likely you could get a look around if they are shut down in the field. If the APU is running, then they are probably busy or at least occupied (unless its Freezing cold and are running the heating!)
Most of the crews of the CG 92's are really nice, personalble guys (and ladies) so if you get a chance to say hi somewhere when they have the time im sure they'd be happy to give you a look inside the machine. Alternatively, ask to visit the base!
(Disclaimer: im sure the 139 crews are great too, but not met many of them!)