New Headlights?

Crackedback is right about relays and he's a good man to see for 'em.

Headlamps dim gradually with usage; new ones are a good idea even if the old ones get brighter with relays. The H6024 Night Hawk is about the only 7" round headlamp that is both cheap and decent. The Hella Vision Plus is less cheap but more headlamp, especially if you use these bulbs in them. Lamp aim is by far the main thing that determines how well you can (or can't) see at night with any given set of lamps, so it is well worth your time, money, and hassle to get the lamps are aimed carefully and correctly with an optical aiming machine per this info; sealed beams are the "mechanical aim" type (use "VOL" specs for the Hella units).

Also think about the other end of the car; see here. Be careful and skeptical about "LED bulbs" sold to replace filament types; almost all of them are useless and unsafe (that includes all of them sold for headlamps). For smaller lamps there are a few good ones; these work well in brake/tail lights and these work well in back-up lights; you will need to install this new flasher (2-prong like original; connect its ground wire conveniently).

Note there is no LED bulb that will work effectively in the front turn signals of a car (such as a '66 Dart and many but not all other A-bodies) that has Fresnel-type optics -- that's the kind where the lens has a central round bullseye with a series of round rings surrounding the bullseye.