I have read past papers on French negation and it says that it is accepted that the NegP in French is null, and "pas" is specifier to NegP. So what would "ne" be then? I haven't been able to find anything apart from it acting like an adverb, but nothing specifying if it is the head of an AdvP
Check this: http://www.bu.edu/linguistics/UG/course/lx522-f03/handouts/lx522f03-9a-ammt.pdf Other than in your mentioned papers though, < pas > here is not in a spec position. It is adjacent to < ne > here (by movement).