Well I think I've jagged it. After unsuccessfully trying to manufacture yoke bearings using plumbing fittings I lashed out and bought pillow block bearings to do the job properly and the result is more than pleasing. Dual yokes move in unison with absolutely no play due to the bearings and simple wire trace connection between the two (idea pinched from Gwyn).
Here are a few pix with more on my website and in the photo gallery here. I've also made a short video of them in action which you'll find on my website.
Gad it's great when it comes together!
Ken.