17 inch Mustang rims..

I believe the wheels with 5.72" backspace are from `99 through `05. After `05 they went to a 6.25" backspace or there abouts, which with an A-body rear would likely require about a 1.25" spacer
When I was running an A-body 8.75" rear, I used 3/4" billet spacers which worked fine with 5.72" backspace. The 8.25 rear appears to be a little tighter (narrower) but will still clear -as per my friend's car who ended up with my old wheels and spacers-.
Also the center registers on ford wheels is smaller, so either the wheel registers need to be made larger or the hubs will need to be cut down.