I have made some progress. The wiring in the left hand toolbox is complete but needs to be cable-tied and tidied up a bit. The attached picture shows the various assemblies, including ignition switch, blade fuse holder, isolator switch and a kind of Christmas tree style junction box that I made. I will need something similar at the headlamp end to distribute 12 volts where it is required. "How come RE manage without such doohickeys?", I hear you ask. Well, their wiring nodes are hidden in the harness in the form of taped up butt joints...
I have also installed a new combined regulator/rectifier unit under the seat. Got it "buy now" off Ebay for about 25 GBP. All the main wiring runs up to the headlamp are in place. The next job is to merge the separate AC and DC alternator coils and hook up the reg/rec.
Things I have learnt:
1) A home brewed rewire takes ages. I have put in about 15 hours so far. I reckon I will need at least another 10 to complete the job.
2) All those extra little bits and pieces you need are expensive when added up. I have spend around 30 GBP on connectors, wire, shrink-wrap sleeving and other odds and ends.
3) My shed is cold!