The flint mines I can believe being more recent, considering the Druid's Rest being medaeval, but the Cursus being a road makes no sense.

It goes nowhere and does it up the very steepest part of the hill, when there are two easier alternatives which can get you to the same spot.

The Cursus widens out far too much at the bottom to be used by a wheeled vehicle in my opinion.
This is not shown very well on this map:

http://www.homeusers.prestel.co.uk/aspen/sussex/wilmington.html#arch2

but is on this one by Rodney Castleden:

http://www.themodernantiquarian.com/image.php?image_id=14504

Whatever one thinks of his Cursus theory, this is the more accurate representstion of the Cursus.