Needing help fora bass Dulcimer

little over a year ago I made a TMD with out going back and re-measuring, I am thinking it has a 28" VSL I have always had trouble bringing it into tune like a normal Dulcimer I have to tune it a Octave below stander tuning. I been thinking and of Just going ahead and making it a bass TMD.

I need all the advice I can get on fret spacing to string gauge. I am pretty sure I will need to change out the tuners. The box is 3/4 maple with 1/4 top and bottom. I am pretty sure that part will hold up for this change.