Some guy on ebay made me a custom order of leds for close to $20 to my door. 100 of them mixed with colors, even some that change on their own rgb. Each was prewired for 12 volts with resistors.
I went this route because for the same price I got 3 bulbs from the local kragen that popped into stock locations and they were not very good.
leds can be awesome depending on the application but don't spread light all around typically like a bulb so you need to tinker with them, perhaps sanding and diffusing their beam, and also you can mess with colors and/or soft/bright white light and other things to diffuse and spread the color. Like those clear plastic colored folder inserts they sell.
I suggest tinkering in a real world situation as far as dash layout, parts and distances and test out each phase. Temporary mount the lights and/or use some junk parts.
These leds I got are waaay brighter than the stuff I got in the store. I was very surprised to find a single led being able to easily brighten up each knob on my old vw for example.
I didn't move over to the truck yet because I think it is blown up and I want another, but this is one of the first things I would do for an aging dash.
My old 85 vw jetta also had leds in some dash indicators and all this time later they remain bright, clear and uniformly lit when on. Everything else though I had to deal with the same as the truck. Certain colored parts, old dirty parts, etc.
I personally like the bright and pronounced knobs with different colors on my dash, but can easily see how you can mess up with spotty and too bright of a light on the speedo, etc. area.
, I've never seen a Merkur that had everything electrical functioning properly...and that includes LOTS of them my two friends have had over the last 10 years.
