I've never heard of Robert Bryan as a North Carolina builder. But with over 400 builds he had some superior building skills. The veined, leaf shaped tuning pegs, the laminated layers of light wood between dark on the tuning head and fretboard, and skillfully cut sound holes are nice touches. Probably built in the 1970s or 80s -- no 6+ or 13+ frets common to many post-Revival instruments. Or perhaps he just liked the older ways of playing.
I'd suggest keeping it "as is" rather than trying to retrofit 6+ and 13+ frets. Playing Chord-Melody style tuned DAd would not be easy unless you are willing to re-tune. Probably best to tune to DAA or even CGG and learn to play Fingerdance or Noter & Drone style.
Have you tried finding the builder's obituary on line? "robert bryan dulcimer raleigh" should be a good google search string. An obit will often give you interesting information, likewise listings in Ancestry and similar sites may gain you more data.