the bolt pattern is the same, try it and see if it looks ok...
also turn the front from lock to lock and see if anything touches.... lift up one side to cycle the suspension and see if they clear...
if it looks good, take pictures and post them up and show us how it looks.
BTW, your grandprix has a bolt pattern of 5x115 and the mustang wheels are 5x114.3
they are close enough that they fit, but they aren't quite right and not recommended.