Ok, here's what I suggest to help brightness. See the attachment for reference as this applies to rallye gauges but should also work for any cluster.
1. See those blue diffusers? Take them out and clean them very well. the dirt that collects in them over the past 50 plus years blocks light. Also, the old plastic gets cloudy with age and also blocks light.
2. Make sure when you put the blue diffusers back, they are sealed up tightly so they don't " leak" light.
3. Paint the whole inside of the housing bright white to increase reflectiveness
4. As was suggested by 65TerrorCuda, replace all the bulbs with Leds . they will last way longer than incandescent bulbs and are brighter.
5. Clean the gauge faces and the white markings on them.
6. Polish the clear lenses.
View attachment 1716210015
