That's a good point about the causeway -- if the Sphinx hadn't already been there, why that route? Jean-Pierre Houdin actually has something of an answer to that, but in most respects he's excruciatingly conventional.
The temple (or whatever it was built to be) in front of the Sphinx was initially built of limestone quarried right out of the enclosure, or gap of air around the Sphinx -- but that limestone shows the same erosion patterns, and was later refaced in granite, with the granite cut down to fit into the irregular surface of the limestone. One stone has the tail end of some lines of hieroglyphs, "...beloved of.., ...living forever", showing it was scavenged from some other structure. The granit itself was still later pulled off, probably since the muzzie conquest.
Since the paws and front legs of the Sphinx, its tail, and so much else of its lower surface are constructed of small stones quarried and sculpted for the purpose -- and these are of all different ages, including quite modern date -- I very much doubt that with the information available the Sphinx can be said to have been a sculpture at all, prior to the New Kingdom. It was probably just the source of large, quarried stone, such as those used for that temple. Based on subsurface weathering, the rear of the Sphinx was carved out about twice as long ago as the front, which pretty much clinches the idea that, even if it was originally a sculpture, it wasn't anything like what is there today.
Among conventional Egyptologists, the view that the Sphinx bears the image of Khufu (it is clearly not Khafre) has started to catch on a little, and JAW pointed out years ago that a New Kingdom copy of an Old Kingdom inscription indicates that Khufu repaired the Sphinx.
The candidates for recarving the face and head to resemble the pharaoh are, IMHO, from either the 18th or the 27th dynasties, as the Sphinx was excavated by Thutmose IV (he erected the Dream Stele to tell posterity all about it, and to prop up his claim to the throne), but OTOH the physical characteristics of the face are more African, and the 27th dynasty was Nubian -- and those pharaohs really liked portraying themselves as sphinxes.
The documentary with West and Schoch is at the link below -- I hope it's not the version with Richard Hoagland and the other fringer who gets started on extraterrestrials while mentioning the "very unique inscription" that talks about Khufu's repairs.
