>> Or am I just being Southern-England-centric about this?

Possibly. There is the small possibility that Ballynoe was actually a passage tomb kerb in an even earlier incarnation. A few 'typical' passage tomb goodies were found when it was excavated. I'm not sure about the timing of the barrow. You'd have to check the excavation reports. There was a small cairn beneath the mound. Several <i>baetyls</i> were found between the inner stones and this cairn. All the pottery was Carrowkeel ware. Both Baetyls and Carrowkeel ware are passage tomb stuff. There were cists at the east and west ends which contained lots of cremated bone. The mound itself was compared by Estyn Evans to Millin Bay (also in county Down, but was reburied after excavation due to its fragile nature - excavation pic available if anyone wants to see it .... it's mad!!!!) Evans also notes that there's nothing like Ballynoe as a whole.

Fun thing about Ballynoe is that it has an almost identical layout to Swinside and it's on the same latitude.

This one's great:

http://www.themodernantiquarian.com/post/43051

It shows all the outliers brilliantly (all the other stones in the field are markers.)

Burl has a good section on Ballynoe in his book which I was reading over New Years before my trip up there. I'm not really equipped to critique what he has to say so I'll just summarise:

Burl believes the circle came first, then two cairns/passage tombs were built inside possibly after the abandonment of the circle or friction between the tomb builders and circle builders (he cites Brats hill, Arbor Low and Callanish as examples). Then some time later the two cairns were destroyed to create the long mound. Because of the similarity between the circle and other circles in Britain which have no features inside the most likely scenario is the circle came first, such as at Bryn Celli Ddu where the circle was destroyed to create a passage tomb.

"The present author believes that there were four distinct stages, an initial stone circle followed by atwo prehistoric phases of intereference and alteration culminating in historical robbery"