Per Woodys Fairlane site.
Width: all measurements are flange to flange
67-71 Comet, Cougar, Mustang, Fairlane = 59.25 inches
65-66 Mustang = 57.25 inches
67-70 Mustang = 59.25 inches
57-59 Ranchero and station wagon = 57.25 inches
77-81 Versailles = 58.50 inches
1957-64 Ford = 57.25 inches
I used the drum brakes from the 8" rear that I removed from the car.
The car is in Florida @ my Dads house right now. So I'm unable to measure it.
With the right back spacing you should be able to get a pretty meaty tire in there. I would roll the fender lip if the car hasn't been repainted yet. Mine are not rolled, You can get a finger in between lip and tire though.
And if you take a tire off and look up inside the wheel well you will see a lip where the wheel house meets the frame rail, I would suggest massaging that area back to prevent any cut tires.
Jet