Earlier today I came across a design for a Stick Dulcimer or Pickin’ Stick. This is a drawing that I made for my use in 2012. It isn’t very pretty, but gives dimensions. The PDF file link is made to print at 11X17 paper size to the scale shown. It will supply basic information, hope it is helpful.
For a better source of information check Amazon for John Ressler’s book titled Pickin’ Sticks Building a String Instrument !