Originally Posted by
Simon Barden
That bit behind the neck pocket carries most of the stress from the strings, certainly all the force that's not taken up by the neck screws. Exactly how much will depend on how the screw holes are drilled and how well the neck fits in the pocket etc. So I'd be wary of cutting and moving what you already have. I'd be happier cutting and sanding another bit of wood to fit in the gap. A spindle sander would make that quite an easy task, as you then only need to trace the curve of the rear of the neck pocket and the curve of the neck heel and place them your selected distance apart and sand to the lines. Epoxy glue will fill in any small gaps at the rear.
Your pickguard should then be adjusted to cover it up.