ORIGINAL: SlideWRX

The hub diameter may not be correct. Mustang hub is 70.6mm. If it's smaller than that, the wheel won't bolt up flat to the face of the hub. if it's larger than that, it will bolt up, but hub rings should be used to keep it centered. I happen to have summer wheels with 73mm hub, and torquing them down in the proper star pattern keeps it vibration free.

Tom

edit: The stock 17x8 wheels are 45mm offset. The V6 16x7 are 39mm offset. Generally, one could run 25mm offset on an 8" wheel without it sticking out.