You want to be looking for a reasonably tight fit and that when in the pocket, the centreline of the neck is aiming for a point halfway between the two stop tail stud holes. Or you can run a long steel ruler down the side of each neck to see if the continuation of the neck line ends up an equal distance from the two stop tail holes. If there's a significant list to one side, then you will probably need to work on the neck fit a bit so that it is straight. I'd use the stop tailpiece holes as the bridge holes are offset, so the tailpiece holes are more reliable.

There are normally no problems with the neck fitment, but it's worth checking, as any remedial work need to be done before any sanding and staining/waxing/painting.

You'd also want to check that the bottom of the neck heel is sitting flat against the bottom of the pocket, and not angled with a visible gap at one end. This is normally caused by one of the pocket sides not being as straight as it should be, and can normally be cured by a bit of sanding.