Right, so after much confusion and advice and surfing, I sussed what the contributor in the Articles section was on about.
Here's my attempt, which hopefully is a reasonable illustration:
Points to note:
1. The mic holder plate wotsit was from Maplin http://www.maplin.co.uk/Module.aspx?ModuleNo=31247&C=Maplin&U=SearchTop&T=MIC%20HOLDER&doy=1m11
2. The straplocks are Schaller. Was very pleased to find I could place them in such a way that I could use the existing screw hole in the backplate for one of the buttons, and not need to screw into virgin Agathis.
3. A major prob was that I couldn't tighten the mic holder into the necessary straight position, so the thing was loose and swung like a pendulum do. I had to put a couple of rubber plumbing washers on the thread so I could tighten it up in the right position (i.e. the top hole of the 3 where it attaches to the pivotty wobbly bit).
4.The other big prob was the angle at which the thing needed to be fixed. The weight of the bass meant it kept sinking to vertical, so I wedged a little electrical connector thing into the pivotty wobbly bit. There MUST be a more reliable and elegant way of doing this, suggestions welcomed.
Hopefully the pics explain this better than my words do.
None of this makes me play any better.