Is this a suitable replacement led for my atlas Gp60 headlamps and numberboards ?

I would not get white,I would get warm white 3mm. (Unless you like the harsh blush tone of bright white).  I assume 3mm will fit,it does for most head lamps. A resistor 470 ohms or more quarter watt or more should work from 12 volts input. 

LINK

Dale H

Here is one circuited from track voltage. 

LINK

They come from China and it takes a few weeks. I never had trouble getting them. If you are in a big hurry,Email me,I will send you a few.

Dale H

Not sure what the question is. The resistor size depends on the input voltage. From 18 volts track power with a capacitor used you need about a 1200 ohm or more half watt resistor. From 12 volts regulated,470 ohm or more. The CL2-n3 chip,if used instead of the resistor will take any voltage (a few volts more) over the LED input necessary to drive them. In conventional you must size the resistor for the maximum input voltage. The LED will light down to 5 volts but will dim. The CL2-n3 chip is constant intensity in conventional. 

Dale H

Here are a few pics of better quality.Click to enlarge

Dale H