I would take the sap wood down as well. Its a bit much for the weight bow you are making. Its not that hard to chase rings in yew. Yew (
I mean you) sorry for the pun, its early.......just need to use a shap cabinet scraper and go real slow, one ring at a time.
As far as the bow design goes. I would make a nice bend through the handel elb out of that piece of wood. It looks nice and straight and would certainly make a nice one. That saw mishap may cause you some problems though it looks pretty deeply cut into the profile.....if its not to bad you could use that angle to then make your D section. Its hard to tell from the photos. For a nice elb blank try this.
Centerline 1 1/8", 5" out 1 1/8", 10" out 1", 10" out 7/8", then taper to the tips to 9/16". For the depth make it easy and go centerline 1", 5" off 1", 10" off 7/8", 10" off3/4" then taper to 9/16". Get the bow to that point with square edges then round your D belly and ease the edge of the back nicely. That "should get you a nice bending start. The rest will be tillering. You may need to shave the whole thing down a bit once you start the tillering process.....that will largley depend on the wood. This lay out should give you a bit extra meat in case you need it.
Understand that you need to look at those numbers as a staring point for your design. Every piece of wood is different and will behave differnt. Every bowyer works differntly. If I had that sitting in front of me that is how I would lay it out.
SJM