You can pick just about any size, shape and color LED you like. Any of them should last longer than your plane when you run them at the typical 20mA. If you're using 4.8V ignition battery packs, then wire the LED in series with a 250 Ohm resistor, across the (+) and (-) terminals. That's it! 300Ohm works better with 6V battery packs to give the standard 20mA load. Really though, a few mA more or less is not gonna hurt the LED.

I typically use water clear ultra-bright red LEDs and aim it directly toward the front angled upward a bit, where I would normally stand when starting the engine. The clear ones are a lot easier to tell whether they're on or off in bright sunlight.

I do this for both onboard glow driver ON/OFF and gasser ignition kill switch.