As you see by the title the bamboo split that  I was steaming before it was flat enough to be used as an one piece backing. So here's my thought sand until thickness 1/16  get the split edges squared off  then take Black Walnut 30 * 3/8 * 1/16  lay BW in the center of the bamdoo glue to ash lam. 30* 2 * 3/32  Second part of question before or after bending ash

Jerry