Also the constellation of Orion probably wasn't recognised as a whole thing in 2500BC the Belt is very prominent and was probably the main thing noticed. The fact that other stars followed the belt around would have been seen, but may not have been important.

How big is the top henge in nigel's composite? If the stars are superimposed over the henges then this one is 10% out. That's fairly inaccurate for a people with advanced maths skills, but the maths isn't the issue.

I've been trying to think of a 'primitive' way to measure them. Can't think of one. Today I could look through a sheet of glass and mark them onto it. Enlarging this would be fairly simple, but how accurate would it be? Not too bad I imagine.

Of course, as it's symbolic it doesn't have to be highly accurate. As long as it gives the right impression that's all that matters. Or is it? Another of those things we'll never know for sure ...

I'm firmly in the 'Maybe/Probably' camp on this.

pedant's corner:
But I wish the question had been "Does Thornborough Represent The Three Stars We Today Call Orion's Belt?", because it doesn't represent Orion for one thing and I doubt that they were called that 4500 years ago and Thornborough certainly isn't three super-hot balls of gas millions of miles away so it can't BE Orion's Belt.