I just read http://www.shef.ac.uk/content/1/c6/02/21/27/summary-interim-report-2006.pdf, and towards the end they say they have had to re-evaluate the sarsen date at Stonehenge because Atkisnon screwed up by dating a later pit in front of 56 as the ramp for the stone itself.

Atkinson's report should be a feature on Red Nose Day. The guy was a clown.

But there was definitely a pit, which could have been dug to sink a stone into, though dated now at 200 years after 56 was raised.