640mm or 650 mm?

The 9 braces Hauser fan is the most thoroughly tested fan brace setup on the planet. It is the result of many years of experimenting. It is braced on Torres 4 fan brace design. The braces act as sound vibrations highways...they carry the vibration of each string to a specific spot on the soundboard. If you put your fingers on the soundboard as you play the 6th string for instance, you will feel the upper portion of the top vibrate with more power than the rest of the top.  You will be able to feel this vibrations with your fingertips all the way to the 4th strings. It is harder to feel the vibration caused by the treble strings. The variations on the 9 braces fan is enormous. Luthier taylor each fan to achieve a specific sound and match the instrument with the rest of the woods used in the construction. Above to the left is a 9 braces all Spruce fan. I often use a mixture of Cedar, Spruce and Mahogany to match different wood combinations Image to the right.

Radiused or flat fingerboard?
The radiused fingerboard has been around the acoustic and the electric guitar since day one. The same is true for most instruments of the Stringed family of instruments (violas, violins cellos, bass). Radiusing (image above) makes barre and left hand stopping A LOT easier. The only drawback is that you will NEVER want to play a  flat fingerboard after that. If you are having your custom guitar built, I am all pro radiusing the fingerboard.  The standard fingerboard is flat.