Hi Ron,
I’ve worked out the dimension, but measuring the hole centres and the od of the hub drive gear, less the depth of its teeth. I’ve also sourced what should be a suitable gear to make the drive pinion from. I’ve kind of had to make a guess as to the depth of mesh of the two gears. If someone knew the od of the pinion drive gear, I would know if my guess is correct or not.
The object of the exercise is to drive the speedo, so achieving that is my main aim, but it would be nicer to know that I’ve made an accurate copy, if that makes sense?