The rising sun travels north and the setting sun travels south if I recall correctly.

Rhiannon is correct. The setting and rising points of the sun will travel south after the autumn equinox, slow down and hit their southern limit at the winter solstice and then come back north once again, through the spring equinox position, eventually to the opposite limit at the summer solstice.
The rising sun will head south every day, reach its mid point and curve back north to set on the opposite horizon to the west. A 'c shape' would be a good way to describe it.
A great route to baking your brain with this stuff is Clive Ruggle's 'Astronomy in Prehistoric Britain and Ireland' or Douglas Heggie's 'Megalithic Science'. If you really want to hurt try Thom's 'Megalithic sites in Britain'.
g.

"Im not sure it this the second chamber was open to the east originally but it looks like a pretty good fit for the equinox sunrise. It may be just a coincidence but if say the east end of the chamber was open but the rest closed off it would surely light the small chamber completely on the Equinox?
"

It would depend on the horizon to east if the sun shone into the chamber sufficiently to lighten it , i.e. the sun rises due east at equinox but if there are hills in the way by the time it gets above them it has traveled further west and therefore not shining straight into the chamber but from an angle .