The new linkage fits a treat.
Putting the steering back together I found why the horn had stopped working. The wire was no longer attached to the slip ring at the end of the column. I tried to resolder the wire without taking the slip ring out. Silly boy. Had to drift the ring out. Much easier to solder the horn wire onto the slip ring with it out and held in the vice jaws.
The last time I was dealing with these parts I seem to remember it just falling out. I wonder why it was sticking this time - how can the top of the column shroud have changed shape?
I finished putting all the switches back into the column. Will complete the rebuild tomorrow night.