The size of the securing nut might vary depending on source. However, I found that a 3/8" sq. drive 3/4" AF crowfoot worked perfectly to both slacken the existing and tighten the new. No doubt the metric equivalent would work too. Quite possibly the original is a Whitworth size.
Modifying a spanner like that shown is an excellent tip though. Particularly the "ring" end. If a, readily available, metric spanner fits then that would be my preferred over vandalising an Imperial or AF spanner.
I don't know whether access in the earlier pull start cars is better. Once the l.h. glovebox liner is removed access is fairly easy.
Right on cue too, my choke cable needs replacing, it doesn't lock any more.
The cables are different lengths too, depending on pull start or key/solenoid start.
I can only think of four "tools" I made/modified.
1. A brake master cylinder cap to enable the use of a pressure bleeder.
2. A starter motor Bendix spring compressor.
3. A 1/4" drive deep socket to install and remove rear brake beehive springs.
4. Front seat webbing "stretcher" contraption.
