To sum up the Wise Words thus far expressed...
1. Replace aged headlight beam selector switch and upgrade to solid state voltage regulator if not already done
2. Perform ammeter bypass, then install headlight relay(s)
3. upgrade aged, obsolescent low current alternator to at least 60 to 100 amp one. These can be had in roundback form factor or squareback at least for over 60 amps/
4. If the perfectly good old DOT approved incandescent PAR sealed beam lamps of the C body Era don't then produce enough light for you, one can buy some dangerously over bright LED lamps which can fit the older 5.75" round sealed beam form. This last step is the only one I won't do for myself, being ecstatic over how well my NOS Westinghouse 400X low/high beam lamps work after having effected Steps 1-3. With plenty current, the old school lamps shine very nicely, and at the proper spectrum for human eyes at night, unlike most of the modern lamps. The spectrum from LED lamps has to be produced from discrete sources, which don't overlap so naturally as the crude but effective Edisonian method of heating wire filaments to incandescence. I usually like quantum effect light sources for most purposes, but not driving light.