Sound, space, two different things. Got it.  I do not have a sophisticated ear so I doubt I would hear a difference.

Thank you for the information.

An arched fretboard has no effect on the volume of the box.  It does free up a couple more square inches of top to vibrate.  But unless you have sophisticated instrumentation you'll not hear the different, IMHO.

The fretboard has 5 arches between the nut and strum hollow with an additional arch between the strum hollow and tail. Would that help to boost the internal volume and bass-baritone response? I've heard the arches increase overall volume a bit. Would the arches make it respond like a larger instrument though?

The dimensions aren't bad for turning into a baritone, especially the 29" VSL.  Although 3" deep and 6" to 8" wide body would be even better (larger internal volume given a more bass-baritone response.  The heavier strings should not damage anything.  I agree you should stick with a floating bridge.  That simple compensation can make an audible difference.

You're very  welcome.  His video opened my eyes to the floating bridge too.  I found it really helps with the longer VSL's.

Thanks for sending me to the video. Now I understand why that bridge is at an angle instead of straight like the bridge on my other dulcimer.

With a floating bridge you are able to tweak your tuning a bit.  Pristine2 has a video posted showing the technique.

Why would you stay with a floating bridge? I am a newer dulcimer player and not aware of the pros and cons to floating or fixed bridges.

The size sounds ok for a baritone.  The slots in the nut and bridge will probably need to be widened a tad to accomodate the thicker Bass and Middle strings.  I would personally stay with a floating bridge.

I am the delighted new owner of a cherry, with maple or fir top, hourglass dulcimer made by CB Henry in 1993. It is a gift to me from the original owner who bought it from maker, but never played it much. Since it is my second instrument, and I really like the sound of a baritone dulcimer, I am thinking about turning this generous gift into a baritone. I wonder though, if it is a good size for a baritone. The VSL is 29 inches, the body is 2 3/8 inches with the arched fretboard adding another 3/4 inches. The top of the hourglass is 5 3/4 inches and the bottom is 6 3/4. Could the thicker strings needed to make it a baritone damage the instrument in any way? I plan to have a 6.5 fret added and the action dropped. The current bridge is a floating piece of dowel. The new bridge I'm told will be glued in place.