The parchmark of the stonehole is visible in Sharpe's aerial photograph, and can be made out in the more recent one by Adam Stanford:
One of them is: "Stonehenge Station-Stone rectangle and the relevant sightlines and horizons: Most southerly moonrise/ most northerly moonset and Midsummer sunrise/ midwinter sunset".
The four station stone positions are in a rectangle that on its longest edge just grazes the sarsen circle and seems to be aligned to astronomical features as above.
Station stone 94 has recently been marked with a handsome polished sarsen stone in a stainless steel ring.
From the public path the sight line to the fallen Station stone 91 should be very close to the sarsen circle. On a visit this week trying to align the marker left a large gap. My hat indicates a closer position which seemed to match the plan and photos.
Click any picture to enlarge.
It would be nice if someone with more time and the right equipment could check if the marker position is correct or not.
See also: http://www.sarsen.org/2015/12/the-position-of-stone-hole-97.html