let's see, I'm at work so I'm going to try and remember as much as I can. There have been so many freak'n dimensions, angles, etc....I will never build a backplate again!
It's a project for mad men!
The jp strap overhangs are 1.5" wide, the center area should be 7"-7.125", and so the outsides are approximately 2"?
And I checked that other dimension you asked for between the back of the neck and the bottom and it came out to 16.75"
Does that work?