These guys have provided you with the correct information. They will physically fit onto the car because the bolt pattern is the same. However, the offset is +30 all the way around, compared to 05-09's that have a +45 offset in the rear. The wheel/tire won't have the same flush fitment you would get if you had the correct offset.
We do offer FR500's for the 05-09 Mustangs. Is there any reason why you're not interested in them?