Instruments of the violin family only has 1 brace. The bass bar. Its below the bass side foot of the violin bridge.
Its standard procedure to use chalk to fit the bass bar. You put chalk on the inside of the soundboard and rub the bass bar over it. The you cut away the parts of the bar where there´s chalk left untill you reach a point where the whole bar has chalk on its gluing side. Then its ready to be glued.