OK, little bit of further information since we've announced the re-staging of the US Airmail Pioneers PP event.
First off, a further MAAM advert because I think it's that good.

Secondly, if you install it into FSX and apply their FSX fixes, you may find that you can't get the engines fired up. If that's the case, just open up the aircraft.cfg in the DC-3 Passenger folder and find:
[piston_engine]
power_scalar=0.83
Replace it with:
[piston_engine]
power_scalar=0.97
And you should find everything works as expected.
Finally, Robert's excellent museum repaint for this plane (in FS9) works in FSX; unpack it to a temporary folder, then go into the DC-3 Passenger folder in your SimObjects\Airplanes folder and copy the default texture.ual folder to texture.ehm, then copy the contents of the temporary texture folder to texture.ehm (overwrite as necessary). Finally, copy and paste the contents of the temporary aircraft.cfg into the default aircraft.cfg just after the second ual texture set. Have fun all and see you at JFK!