RR - sorry if this goes off at a slight tangent, but it is kinda related.
Neil, I know you're running ducting through the vents to the arch liners - can you say you noticed any marked difference in brake performance? My thoughts would be there's too much turbulent air in the arch being generated by passing flow and the effect of the spinning wheel, so they could be refined to give better effect.
A lot of the MKI/MKII lads are running carrier ducting direct onto the disc. I'm also looking into this and am in the process of supplying hub measurements/photos and caliper locations - do you think it's something you may be interested in too?... or, anyone else for that matter.