i ahven't doen it, but have considered it. The only real problem I can see (or can't see, which is the issue) is that LEDs work best as direct illumination. Guages tend to be back-lit, so they may come up as very dim as there won't be enough scattered light to illuminate the guage. I have seen on one site (can't remember which one, but I think it's in the Links) that has LEDs for dash lamp illimination. They have a wide angle LED cluster, I recall that they migh even have them pointing to the side, too. Might be worth checking out.
If you do it, and it works out, let us know. I may consider it, too.
OT, I have used LED lamps, the ones the kiddies use on their ricer cars for lighting under the sills, as under dash lighting. Works very nicely to add some light in the foot well area. Not too harsh, just enough to see.
