Well, you learn something new everyday! I focused only on the "B" measurement shown above, the length of the front lower fender from the wheel opening to the valance. The "A" and "C" measurements would be different car to car, and possibly even a little bit side to side with adjustable strut rods. The D measurement was the same on both fenders so I ignored it too.
So, I have a bunch '71 Dart fenders because I have a few '71 cars. Since I have easy access to several of them I pulled some measurements. My Duster has '71 Dart fenders as part of it's Demon conversion, plus I have my butterscotch GT handy, plus a pair of extra fenders I pulled from another '71. All of those "B" measurements were the same at 8". That's 6 fenders, all OE, all '71, all measuring 8" for the "B" dimension.
I also have a couple of '72 Dart fenders (I was collecting fenders for my Demon clone for awhile). Both OE, both passenger side fenders. The "B" measurement on both of those fenders was just under 7 1/4".
So, if the 8 OE fenders I measured are of any consequence, the "B" dimension may have changed somewhere between '71 and '72. What do you know about that fender? Any chance it's had work done to it?
Also, just for reference, a 225/60/15 on a 15x7" OE cop rim isn't a slam dunk for fender clearance on these cars. I had to adjust my lower fender to bumper brace all the way out to clear them when I was running them on my Duster.