"If it has we have the interesting situation that if it was more bent previously then the pyramids may be spot on whereas if it was straighter then Thornboro is. "

Perhaps it is yet to become more straight and Thornborough's time has not yet come ...

It depends on where we are in the precession cycle as to whether T'bro or Giza have the closer alignments. The period of precession is about 26,000 years. Hancock would not have looked into the future to find an alignment, so the fact that he had to go back almost half of the total precession time means that T'bro may well have a better alignment by only going back say 5000 years.

Actually, thinking about precession, it sounds like a load of crap that the stars would look any different. There's a much larger parallax change as the Earth orbits the sun than would be observed as a result of precession. If there is a change in the shape of Orion's belt it must be due to Proper Motion of the stars themselves, so Hancock's idea of change due to precession is a load of bollocks.