The regulator does NOT have anything to do with your dashlights. The voltage regulator is only for the fuel and temp gauges.
Probable culprits are bad bulb, dirty contacts, bad bulb holder, bad trace on circuit board. I don't remember how much harder it is to pull the instrument cluster on a dart than a valiant, but 65 valiants are easy to pull. I would pull the cluster out clean copper where the bulb holder makes contact, clean the terminal pins where the harness plugs in, and clean the copper where the circuit board bolts to the dashface. The little nuts that the factory used are stamped steel with a very small contact area I like to change them to normal style nuts with small copper washer and some dielectric grease. And while you have the dash out replace every bulb so you don't have to go back as they fail one by one.
