>once stripped I will compare it to the wiring diagram to see if a standard replacement will work or make my own.
>If the latter, then no doubt I will be on for more advice on stockists, connections, type of wiring etc
It's highly-unlikely the loom on your bike is original - apart from anything else, your bike originally had 6V electrics with the shonky Volts and Amps regulation through the PRS8 rotary switch (is that still there?), used before 12V and Zener diodes.
So now you have first-hand experience of pattern looms; ime, 'fraid it isn't unique ...
I've been building Britbike looms for over thirty years, I'd sooner stick pins in my eyes than consider any off-the-shelf harness, even if it was allegedly for a standard bike (which yours isn't?).
I've bought pretty-much all my wire, terminals, tools, etc. from either Vehicle Wiring Products or Autosparks. Never had a problem with standard Britbike bullet-'n'-snap-connector terminals/connections but then I use the easily-available compatible wire, terminals, crimping and joining tools ...
Happy to help if needed.