Have just found a spare Sumlog drive cable (a marine version of a car speedometer cable). If you think finding a NOS A7 longstroke crank or similar might be difficult, try finding one of these (especially one long enough to fit a particular boat). Naturally, the price reflects the scarceness. Of course, they need to be cut to length but, fortuitously, the square at the end is a separate item that slips onto the cable and just needs crimpling in place (using the totally useless tool suplied for the purpose).
What has this to do with our motorcycles? Wel, thinking about this cable reminded me of shortening the speedo and revcounter cables on the project and the need to re-form the square drive. In case it might be of use to others, I thought I'd put together an idiot's guide how to do the job. Attached is my attempt to describe the process - a bit long-winded as I was trying to avoid including diagrams. Those who have even half an idea how to do such things need read no further.
Edit - the attachment is in Word. Adobe opens it.
Also, I see some regret not having a mill to machine the necessary groove in the jig. Fear not - just mount an endmill in your lathe chuck and fasten the job to the toolpost.