To know for sure, you need to determine the following for both the 2012 donor wheels and the 2000 Mustang:
* Bolt Pattern: This refers to the number of lug nuts and the spacing between them (e.g., 5x114.3). These *must* match exactly.
* Hub Bore Diameter: This is the diameter of the hole in the center of the wheel that fits over the hub on the car. It needs to be the correct size, or the wheel may not fit securely. A slightly smaller hub bore can be adapted with hub-centric rings, but a larger bore is unsafe.
* Wheel Offset: This specifies how far the wheel mounting surface is inset or outset from the wheel's centerline. A significant difference in offset can lead to rubbing against suspension components or the fender.
* Wheel Width and Diameter: Even if the bolt pattern and hub bore match, the wheel might be too wide or the diameter too large or small to fit within the wheel well without modification.
You can find this information stamped on the wheel itself, in your owner's manual, or online using your car's specifications and the wheel's part number. Checking compatibility charts online dedicated to Mustang wheels is also a good idea. Without confirming these specifications match perfectly, don't assume compatibility. Improperly fitting wheels can be unsafe.