To turn the text upside down, the key was to reverse the arc.
On the radar I had a look at what pie was returning for my text tracks and reversed the startAngle and endAngle of of the segments that pie() generated
https://talk.observablehq.com/t/is-there-a-correct-way-to-add-an-operation-to-chained-instructions
I still have to do some text positioning work as the text placement is also reversed on the y offset.