I finished a Galax-style dulcimer(picture attached) last year using wormy chestnut, but ran out of wood before completing a double bottom. I've decided to add the double bottom, probably using poplar painted or stained black. My question is the thickness of the spacing blocks and the double bottom. I've seen pictures of Ben Seymour's (Kudzu Patch) and Jacob Melton's (in Ralph Lee Smith's book) dulcimers and read Clare's transcription of Dave Lynch's instructions. Is there anything other than aesthetics guiding the spacing and thickness of the double bottom? Also, since I'll be using book-matched pieces, is there any reason to not use a back brace(1/8 x 5/8 spruce)?