0,0,0 is a standard open diff. I believe LSDs were an option on Ferraris at that time, but perhaps this particular car (it does have a particular serial number in the game) doesn't have one.
EDIT: my advice for tuning, coming from my GPL experience, would be to set everything to 5 on the custom diff, and start increasing the accel setting until you get a nice "adjustability" to the direction of travel via the throttle mid-corner.
If you're oversteering into the corners under deceleration, increase the decel setting slightly or trail the throttle a tiny bit, even (esp.) on the brakes. If you have a high accel and decel setting, you'll probably need a higher initial setting to prevent the car doing weird things as you transition between accel / decel through "neutral throttle", which gives a sort of unpleasant "spikiness".