To to get closure on this, cos' there's nothing worse than doing a search on something finding the ideal thread then finding out the guy who started it never concluded what happened
This was a real easy task!
After taking out the relay board and cutting out all the mounts for it (I needed the area for a dry sump oil tank), I then took apart the plugs on the ends of the 2 main cables that come into the relay board. Using the various circuit diagrams helpfully provided above, I stripped out and binned a load of the wires that weren't actually needed (which from memory was about half). Then the ones that are left (apart from one for the alternator charging light) are simply spliced individually together i.e. they are only pass through wires on the relay board anyway. Use the relay board circuit diagram and the colour coding to figure out which ones these are.
Then lastly I mounted the regulator on the tinware, plugged the alternator cable directly into it, using the standard plug, and simply spliced in the dashboard signal wire.
Simples!!! Took me about an hour.
Now I've got a whole load of space for the tank, simpler wiring, a little less weight, and less concern about water ingress through the engine grill onto that redundant relay board.
Now to take some pictures of the new shiny oil tank