Jost, in theory you could tune any guitar like this, but I am using a guitar specifically made to be a baritone. It has extra heavy strings and extra bracing and a strong truss rod to be able to handle the extra tension. I would be wary of just stringing any old guitar like this. Without that extra bracing, you might do some damage. I am certainly no expert on instrument design, however. The strings mine came with range from .016 to .070. They are pretty big and give my fingers a workout.
Dusty T., Northern California
As a musician, you have to keep one foot back in the past and one foot forward into the future.
-- Dizzy Gillespie