I don't remember what kind of the bulb they had or what the socket looks like, but using LED's is common with 70's-80's Jaguars that used fiber optics and have the same problem. The only problem with LED's is that most cannot be dimmed, but I doubt you'll find a bulb that's too bright. Do you know the bulb number? First I see if you can find a direct LED replacement.
06 classic here. i finally replaced the main light diverter behind the speedo and tach panel the fiber optic just snap in i bought the new piece and it came with the light and socket. i tried a bright led but it didnt seem to help at all. do not put to big of a bulb in the existing socket as it will overheat the main light thing that is what the guy before me tried and it melted it. also you can use q tips and cleaner to the tags therselves that really help too. but even with all this if my panel lights are not turned all the way up it still barely lights up. and cant read them even when on full brightness