Quite possible that they are LEDs at that age, and I can't see it being anything other than 12V DC. My other hobby is vintage audio and LEDs were used for indicator lights right back into the 70s. I was just working on a Yamaha stereo receiver built in 1974 and it has a couple LEDs for power and stereo FM indicators.
In most of the marine suppliers around here, you can buy Blue Sea replacement panel LEDs and a couple other brands (Sea Dog perhaps?) already set-up to run on 12V DC. I know the Blue Sea come with a 'holder' for the bulb and come in different colours. I've used one or two when I'm out of red LEDs or need one-off of some other funky colour for my audio projects! Rather expensive way to do it though! Most of the LEDs I use I go the lazy route, rather than assemble my own, and buy off Amazon .... pack of 50, prewired with pigtail and resistor for $12 -$18, and will run off about 8 to 15V. With the fixed resistors intensity will vary with the voltage. Cheap LEDs, probably not the best quality, but so far they've worked fine. The pigtails are ridiculously thin wire - maybe 28 gauge (but then again so is the wire on the larger red LED I picked up in a marine store for my compass light!). Note that if you are replacing an indicator light for an AC panel then it will run on 120V AC. Blue Sea sells separate LEDs for that, and there will be 2 differences. 1st, the resister will be a higher value and 2nd they will probably have something like a 1N4004 rectifier diode wired in, to block reverse of the AC cycle. LEDs are diodes, but they aren't designed to block a lot of reverse voltage ... they will break down fairly quickly. There may also be a small capacitor in the circuit to reduce flicker (the LED on AC is only lit 60-times a second ... you'll see it flicker if you look indirectly at it). For the DC application only the resistor is needed. However the LED will be polarized, so test it before any soldering. If it doesn't light up, reverse the connection. AC will work regardless of how you connect it.
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