or you could do it the easy way.
cover the neck heel with a piece of tracing paper, cut the outside edges to match the neck heel, mark the holes on the tracing paper, the put the piece of tracing paper in the neck pocket upside down like it was on the neck and you put the neck in, and transfer your holes. As long as your neck fits good in the pocket, your holes will line up perfectly every time. Unlike using pickguard screws or something like that, if you are sure to accurately cut the holes in the paper to match the neck, you can measure to find exact center, screws in the neck holes could tilt and be off center. Not that it matters, you want your holes in the body slightly loose anyway to allow for some adjustment, plus, if your screws are threading in the body holes, you'll never have the neck suck in tight, the screws should be free turning in the body, they are a clearance hole for the neck screws, you only want them threading into the neck.