Great piece of Osage you have there. If you are stuck on a recurve, I would keep it under 60" but that is just me. What draw length are you looking for? In my opinion, draw length at least as important as poundage when figuring the length. I find Osage very forgiving, I think that it is a great beginner wood. I made my first selfbow, my second bow overall, with a Gary Davis Osage stave.
You have access to some of the worlds best bowyers right here on this site, so there is no reason you can't build a good bow the first time. Ask a bunch of questions, and get a little more feedback before you start cutting such a fine piece of wood. Tell us the draw length and we can give you a better idea on length. Post lots of pictures as you tiller and you can get all of the guidance you need.
