Graham...
The index and ATC is all sorted. I went with my original idea of using some of the original gear on the spindle and my own PLC.
The index shown above is for the the carousel only, the original control never used one, but probably used a paremeter in the control and some non volatile memory to store the last carousel position.
Oneday I'll get ome pics up here of the setup. I may even post up my <$10 PLC design

at the moment I'm just too overwhelmed with work.
Wayne...