I've made four from staves, none from boards though. Width at scallop cut outs will depend on wood type, density, length of bow, target draw weight etc. I modeled mine from sketches from book 'bows & arrows of native americans' by Jim Hamm and Steve Alley although my dimensions were different than the book.
Do take a look at Half Eye and Gun Docs post, their bows are very well done representations of this style and Rich
sometimes post dimensions of his bows to help others. He is also has a lot of knowledge on historic bows in this style.
Good luck.