...by lucky happenstance I came across the headstock template from the Nate Bass I built a few years back- it was my first PitBull Bass and can be seen in the demo vid for the JB-4.
The alignment of the Nate bass was spot on, so hopefully this template plan will mean there are no further problems. They seem to line up on the first measure, but I'll be measuring a few more times before the drills come out.