Ok, I did some looking and thinking and my plan A right now is sassafras but I'll be working on a piece of osage as a plan B. Going for simple flatbow style with a bit of reflex and stiff handle with shelf. On the sassafras, I'm planning to go 2" wide or a little more with a slightly rounded belly to take some load off the back but I still think it will qualify as an american flatbow. I'm gonna chase rings and reduce to rough dimensions tomorrow, and then I'll bring them inside to stabilize for a couple of weeks.
Here's a picture of both staves,
and one of the ends.