I looked at my standard and rallye light bars again and I'm confident the standard light bar could be used with a rallye instrument cluster. It might not be too bright in the tachometer gauge area, but I think with some 1000 lumens LED replacement bulbs, it would work pretty well.
The inside of the bulb housings appear to be painted white or silver. Interesting that the standard bar uses 3 each 1816 bulbs (4.3 Watts) and the rallye bar uses 4 each 1893 bulbs (4.6 Watts). I'm sure the LED bulbs would be even brighter than the little tungsten bulbs and pull less wattage.