John,
I'm guessing but I gather that your machine is similar to mine.(Villiiers engine) If so the ignition lead which screws into the flywheel backing plate has a brass button(which contacts against the coil) and a spring. If you remove the button, look up the centre of the spring and you will see a small screw. Use a car ignition cable (cut one end off )with the mowers original attachments. Added bonus is you dont have to unscrew the top of the plug for replacement.
As far as the plugs concerns use a Champion D16. Get them from most auto shops like Repco. Mower shops usually shake theirs heads and start taking about sleaves. This is what happens with antiques. Hope this helps. Let me know how you get on.
Drew
