After I removed the circlip the input shaft came apart fairly easily. I need to get a press, as hammering late at night can't be good for the neighbours, and the shaft will drop out onto the floor when it comes free.
I took the shaft and the motor to Precision Engineering on the shore. They weren't too happy to have a 40kg motor as the only template for the spline -- if it was smaller and lighter they could offer it up to the shaft while it was still in the spark erosion machine. This is important because centering the shaft in the machine is tricky. I've asked Victor if he has any specifications for the spline.