Can't help you with replacement necks, but I can tell you that the truss rod, unfortunately, does not just simply screw out. Replacing it requires a lot of work including removing the fretboard to replace the rod and then putting it back on in addition to other work. Does the whole rod twist in place, or just the nut? In any event, I believe that there is a good bit of information in this section on truss rods if you try using the search feature.
