You would most likely need the following:
-Two Factory HID housings
-New harness for the headlights (not due to turn signal but rather the ballasts that fire the HID bulbs; the distance between the turn signal seems inconsequential)
-Two Factory spec HID bulbs for the housing
You should be able to ground the ballasts in the stock manner, mount them in the same manner, etc.
The biggest part seems to be replacing the non-HID wiring...
I would suggest going to a local Ford dealer that has an HID equipped Mustang and checking under the hood for mounting locations etc.