Hi Oli.
Great minds think alike then.
I ordered 2 hot rail humbuckers from Alibaba.

Thinking of incorporating the 3 way switch to make up to 9 variations.
I don't know the first thing about wiring so it will be pure experimentation.

Did see some humbucker schematics.
This is one that I'm playing around with.
Not at all the 'final' (I haven't put the tone pot in it yet)
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BTW The red is a lot more mellow than in that shot.
Here's a quick mock-up...real life is probably somewhere between that first shot and this one.
Still lots of Tru-Oil coats to go though.
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cheers, Mark.