3 string Dulcimer

Started working on my first Dulcimer a couple of years ago and got sidetracked moving. Now we are finally settled in, and I am starting back to work on the Dulcimer.I bent 1/4" X 1 3/4" ribs of oak by steaming them and securing them in this jig.I have laid out the ribs in the way I want them, and figure the soundbox of the Dulcimer will be about 22" long X 8" wide X 2" deep.I would like the finished Dulcimer to have a tenor sound, and tune the melody string to C or D, and use the other 2 strings as drones.My question is, to have the Dulcimer tenor, what VSL length is appropriate, and what type of wood would be a good choice for the back and the soundboard? I am open to making the fretboard longer if necessary.Regards, David Messenger, formally Ladd