LED conversion go!
Fully stripped the panel and fitted lengths of 12v warm-white LED tape around the inside of the cluster, and it worked out quite nicely. Originally there was a light-pipe that shone a little bit of light down over the front of the gauges, just enough to illuminate the needles; but now I've repainted the faded needles with flourescent paint, I'm considering downlighting it with a little bit of UV just to make them stand out without the source of the light being too obvious.
Also, because I never manage to put these things back together without fucking something up, the speedo now overreads by 10mph, and there's a funny clicking coming from the region of the mechanism. So that's something else I've got to fix next time I'm in there. :)