I disagree with your analysis that the alternator can't keep up with lights and ignition at idle. My 70 37amp after sitting a month or more, will start, and have no issues recharging battery, running ignition, and lights without flickering. There is plenty or magnetic field generated. Remember the pulley ratio. Current drawn from the alternator is based on the load, and it was sized to handle basics at idle. Flickering is not normal in my opinion.