The fluted headlamps only came with driving and parking filaments, no High/Low bulb.
My 1928 has the original 21/3 bulbs in the headlamps, and it's fine for driving at night. You can forget the parking filament and use a dual filament bulb, used as HI/LOW for driving. I think they can be purchased as 25/25, 35/35, or 35/50.