The Violin tie: The tailpiece on a guitar is called for just as it is on every other member of the strings family (violin, etc.). When the first classical 
guitars were built, gut strings were the norm... the tension on these was nothing compared to modern nylon strings. A tailpiece was redundant...
Anchoring the strings to the lower bout meet point, which is one of the sturdiest parts of the instrument, allows the builder to thin the top more 
allowing for  a much bigger sound and not recur to the use of carbon fiber or other non wood materials that give the classical guitar a "plastic sound. ". 

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.

The hand embossed leather case is a work of art on its own right. Built by one of a handful of very talented leather embossers in Latin America. 
Its built following my specifications for the interior to fit Bellucci guitars like a glove. All Plush interior, key and accessories compartment.

640mm or 650 mm?
Regarding 650mm or 640 mm fingerboard fret spacing, keep the following rule at hand: If the distance between the tip of your thumb and the tip of your little finger is equal or less than 9 in. when fully stretched, use 640 mm. Adapting from one scale to the other takes no adaptation
.