I,m gonna be a bad boy now, so don't take this as a suggestion.
I'm actually on strike at the moment, (a one man strike over a matter of principal) so I'm at this computor pretty well all day. (opened the bar pretty early as well)
Anyway I just thought, instead of trying to show what we think stoneage man may have done, why not show what he should have done?
That is erect the whole bloody trilithon to 90 degrees in one go, lintel included. It is possible.