Do I understand correctly, that the four neck screws are just wood screws directly into the material of the neck? I never assume any wood screw can be loosened and tightened more than a few times. As far as I am concerned, when you're dealing with wood screws holding together a stressed joint, you need to put them in there, torque them down, and leave them the heck alone as long as you possibly can. If I had a (normal, not an exotic collector's item) bass like that, I'd be making a recess for access. I think a rigiht angle slotted screwdriver would do fine. Taking the neck loose every time the truss rod needs adjustment seems like a recipe for early stripping out of the screw holes. Putting metal bushings in will be way more trouble than loosening the strings and using a small access recess.