On my 70 Challenger, here are the dimensions using the center of the Pentastar where all 5 lines intersect as the reference point or Center:
From the upper crease line go Down 10 9/16" (Y dimension)
From the left fender edge (where the door gap is between fender and door), go to the Right 7 5/16" (X dimension)
From the right chrome fender trim (edge closest to the tire) go 6" to the Left. (X dimension)
From the bottom crease line, go Up approx 3 15/16" to 4" to the Pentastar. (Y dimension).
A tricky one to measure with the reflection, lighting, etc. I marked the crease line with a small piece of masking tape and checked it several times.
Check:
The sum of 7 5/16" plus 6" does equal the actual measurement of 13 5/16".