If you haven't already done so, just try all your cavity connecting holes for size before you go too much further. Especially your bridge pup hole to the control cavity has to pass two six-core + ground pickup leads plus three or four (four for a switch ground wire if you aren't using shielded connection wires) wires too/from the selector switch, plus maybe one or two ground wire for the cavity foil grounding connections. Make sure both pup cavities have enough room to run the cables through them without getting in the way of the pickups and causing them to tilt or sit up high.

If you need to get a drill or a Dremel out to create some extra or wider channels, I'd do it now.

Hopefully you won't need to - but better safe than sorry.