A few minutes fettling after work this evening - and taking Chris' advice, I took the top off the steering box. I was expecting it to be like an Aprilia, but it is completely different. Instead of a segment of teeth, there is a whole circle. As far as I can see, it doesn't matter where you are on the circle, so long as the steering column and drop arm are in the right position relative to one another. We'll see when I fit it !
The condition of the box was so good, clean oil, no tight spots or anything ,so, I have decided to leave it alone and will just replace the output seal (ordered from Omicron so hopefully will be here soon) and have made a new gasket. Coat of paint and soon be ready to fit .... I am sure the nuts and filler cap would have been black originally, but allow me a touch of individuality .....
The steering box appears to be B10 since the castings say "B10" ! - but it is overstamped with C80 S as mentioned above. Don has informed me that the front axle is B24 with B10 brakes and wheels, so they are a bit of a "parts box" car !