Julian Cope presents Head Heritage

Sure. But on page 68 of Stukeley Illustrated it shows his "View near the spot of the termination of the Beckhampton Avenue" and he both writes and draws "the track of the Avenue" and shows only 4 (prostrate) stones. That seems like he recorded what he saw and didn't embellish it.
I'm sure there WOULD have been a pretty old track there as a long distance track terminates just behind his viewpoint I think, so it would be bound to carry on to the henge. I'm inclined to think his illustration on that occasion was as close to a photograph as he could manage.

What that doesn't tell us though is whether his "track" was an Avenue (stones or no stones) If I was building a stone Avenue I might get a bit peed off at the extreme ends and just mark it with pebbles.