Mikael Carstanjen 1975 Courting Dulcimer - Repair Question
Instruments- discuss specific features, luthiers, instrument problems & questions
What an amazing and even historic instrument! And that seems like a big issue to fix. Just curious, Jim, have you talked to a professional instrument restorer? A quick Google search discovered the Smithsonian Museum Conservation Institute https://www.si.edu/mci/english/learn_more/taking_care/musinst.html
They can give you leads to conservators in various locations in the US and Canada. Not sure if it's financially feasible but they may have some good ideas for you.
Best wishes for your project.
~Bob

I wonder if the owner knows how interested people are of the 'decoration' hanging on his wall!!