The planning application for detailed work at Stonehenge monument includes details of how the Avenue will be marked with a brass arrow pointing to the midwinter sunset and midsummer sunrise axis - http://southplanning.wiltshire.gov.uk/public-planning-application-documents/00537500/00537003_Plan_Views.pdf - The marked axis is between Stonehole 97 and the Heelstone, not over the top of the Heelstone.
Stonehole 97 will be marked with a "stonehole marker" which will look great.
(click for larger)
Here is Mike Pitts' plan of Stonehole 97 and other features, which as he discovered the hole probably can be considered reliable.
Is it me or has 97 moved in the plans?
I also note there is no permanent fence around the Heelstone which please a lot of people.