I love it when a question I have is already answered. This forum is truly a goldmine.
You can just leave off the extra LEDs & resistors altogether if you are not using them.
Bob thanks for posting the schematic. I'd like to use all 3 LEDs in your original design with a 12V input and 5V Vsource as per the OP. I'm also thinking an audible alert with a piezo on overvoltage will also be sensible, though I'm not sure an ATmega etc will hold on for too long in that condition (but at least I'll have a buzzer telling me why it died).
Not wanting to mess this up, what voltages should I expect as "High" at pins 1 & 7? Is it 12V in both cases? Sorry for the newbie question and please feel free to aim me at something that explains the LM358 in simple terms if you know such a resource.