Gauge light bulb spec?

The pre-'66 holders aren't easily available. The '66-up holders take the all-glass wedge-base bulbs and fit the dash circuit board holes same as the earlier holders. Standard # SP500A if your circuit board holes are 1/2" diameter, Standard #HP4090 if they're 5/8" diameter. Use W3W bulbs (e.g., Sylvania 2821) if you want ordinary dim dash lighting, W5W (Sylvania 2825) if you want considerably brighter, WY5W (Sylvania 2827) if you want considerably brighter and a yellower green color (or amber, if you remove the blue plastic balloons inside the instrument cluster).