I’d spoken to Rex and Debb before Christmas and they’d kindly put the relevant electronics in the post. Seems the technology had moved on (a lot) since 1973.
The charging coil now doubles up as the trigger, so its a case of just of connected one end of the coil to the earth on the stator plate and connect the other to the spade connector on the ignition coil. I’d got the grinder out and ensure a good earth for the coil, and got it to fit to one of the existing mount points (this will need further tidying when I get a spark).
Using the meter, I check for continuity from one of the charging coil connectors to earth and then from the other to the ignition coil. All ok. I then checked for earth continuity from the ignition coil to the engine, which was also good.
As the charging coil is also the trigger, its rotational location under the flywheel is going to be important and need to work on this, as currently not getting a spark. There is voltage from charging coil to ignition coil but need to see what is expected.
The one connector on the coil had come away slightly from the coil, so I’d passed a cable tie round to hold it in place. There’s not a lot of room under the flywheel and I may have knocked it after the initial soldering of the wires.
More research and information and hopefully we’ll get a spark. Electrics are not my forte, but on a bike like this they should be pretty straightforward.