Try this for 1b, showing the moat and taken in Feb from the top of Waden Hill:

http://www.themodernantiquarian.com/post/11002

This (again for 1b) shows the first site of Silbury, when approaching the Avebury landscape on the Ridgeway from the south, though the arrow is necessary:

http://www.themodernantiquarian.com/post/10010

This for 1a:

http://www.themodernantiquarian.com/post/10007

All can be provided in greater detail.