Okay, the results are in:
Widths
(in RED)
Overall width: 1.495" - .308 =
1.187" including flyers
Width minus flyers: 1.298" - .308 =
.99"
Heights
(in YELLOW)
Overall height: 1.366" - .308 =
1.058" including flyers
Height minus flyers: 1.037" - .308 =
.729"
Diagonal
(in GREEN)
Diagonal measurement MINUS FLYERS: 1.258" - .308 =
.95"
Best I could do.
This is not an average, like the numbers posted in the OP, I de-skewed the gridlines and overlaid them directly on each other in Photoshop, using the software with guides to ensure the best accuracy possible on an image of this resolution. If I had a higher-resolution image that is not skewed I could get a more accurate measure. Methodology: I scaled the image so the on screen ruler graduations matched the .5" gridlines printed on the targets. I then used Photoshop's ruler tool to measure the extremes noted (minus paper tearing), and then subtracted one bullet width for a true center-to-center measure.
edit: Spent about an hour on it, trying to make sure it's the best I can do given the image quality.
Again, get me a more high-resolution image and it will only increase my accuracy in measuring - I was literally at pixel-level measuring this!