Well, that didn't exactly go to plan! I went and repainted all the carapace with whatever Deneb stone is called these days then flashed over the top of it with a few coats of this snazzy orange. I was pretty happy with that result, but then trying to chip/stipple/spot the edges as was shown in the drawings, impossible! You can't get decent coverage on the back plates without hitting the stacks and it just looks messy.
I've pulled the pin, back to super high gloss black with a blue wash and a bit of edge highlighting I think, I don't like the look of the feathered edges GW does so I will keep it simple.