We keep these spacers in stock and use them on our own S197 Mustang street and race cars.
Don't forget longer wheel studs - Any time you run a wheel spacer you MUST install longer wheel studs. Most track and racing organizations want to see the wheel stud extend THROUGH the lug nut, to ensure a "one diameter of engagement" rule. We use the ARP wheel studs in S197 Mustangs at both ends, but they are different part numbers. These are available from Vorshlag in this same product section, and we sell the Ford Racing front wheel hub kit with the 3" long ARP wheel studs pre-installed. Ford Racing hubs can be found here!