I've just stumbled back into this thread. I am A W Jeffreys daughter (my posts are way back).

Strings: we used banjo strings (2nds and 4ths if I recall correctly?)

I have had many requests for info in the last several months. Much of my memory is poor, but I am certain there is written history of my dad's dulcimer experiences. I am a teacher and have little time to myself at the end of the day, but this summer I hope to wade through my mother's possessions (she died in 2004) and see what I can come up with.
My email is: janpainter3@gmail.com . . . If you want to know what I come up with this summer, just email!