I do not know the actual backspacing measurements but I run 15 x 7 Mustang police steelies with no issue. My 14 x6 Cragar Truspokes stick out just to the fender edge like the 15’s do. My 14 x 5-1/2 Fairmont steelies ride so far inboard I require wheel spacers to keep them off the suspension parts. Your results may vary as I also have drop spindles installed.
Bill Ascheman
Fiberfab Ford
Modified 5.0, 5sp., 4:11
Autocross & Hillclimb
"Drive Happy"