Unsafe junk, please get 'em out of there pronto—seriously. Either put in spec incandescent bulbs or the LEDs I linked, or the (only) other potentially acceptable one for brake lights is
this one (that's the only one that works acceptably if your car has Fresnel bullseye/ring lens optics in the taillights as decribed above for the front turn signals -- I didn't mention it at first because the '66 Dart in question doesn't have Fresnel-type taillights). I say "potentially" acceptable because it's not just a matter of "Yep, they light up and they look nice 'n' bright to me". Any incandescent bulb of the specified type (like an 1157) works acceptably in any lamp designed to take that filament bulb, but LEDs are a basically different kind of light source than the lamp was designed for, so even if it physically fits, even if it looks like it lights up OK, it's case-by-case as to whether it works safely and otherwise acceptably. Please see details
here, then you'll need to assess the performance of the LED bulbs in your particular lamps by comparing them side-by-side with the original incandescents as reasonably well described
here.
Even more detailed discussion of tail/brake/turn signal light performance
here starting at post № 3.
