You've got nice, thick rings with good early/late ring ratio so chasing a ring should be pretty easy if you take your time. Like I said, start about 6" from the end and chase the ring back to the end then go out another 6" and so on to the middle and do the same. If the stave has knots and/or pin knots leave an island of the previous ring around it. If you try to work over the knots you will violate the back ring. Once you have gotten to a good, clean back ring work each knot or pin from the center out around the knot so you don't violate the back. Leave the stave full length until you get a clean back ring then figure out where the bow you want will fit in with the least amount of anomalies. Post pics of the back when you get a clean back ring so we can help you lay out your bow.
If you don't already have shellac buy a can of spray shellac and seal the back as soon as you get to a clean ring. Spray shellac is a little more expensive($8 to $10) but it is more convenient and has a lot longer shelf life than the ready mix stuff. I keep a can on my work bench all the time. Never know when you might need it.
Patience, patience, patience!!!
Remember, you are working with an irregular piece of wood so don't try to make everything perfectly flat and straight like with a glass bow. Take advantage of the character of the stave and work with it, not against it.