After that, the assembly went really smoothly. I installed the 14/14 dellorto SHA carb and last of all fitted my secondhand variator.
The bike idles very well but isn't jetted correctly so doesn't want to run much above idle. Also the stock engine return spring is too stiff which is limitting variation. Here is a video of the crank turning in the cases, a load of pictures of the rebuild, and a video of the engine running.