Red Hill: Depending on how good your stave, design, and tillering are, you can easily get a 26" draw from an unbacked 60" stave. However, the shorter your stave gets the better all of the above have to be. Leaving it wider is a good choice. I've always favored a bit longer bow than needed, but have built a couple in the 59-60" range for my 26" draw. If you're wanting to build a bow to practice your skills, then I'd suggest leaving it longer than necessary. I'd even start at 68" and see where that gets you. If you come in under weight, pike it. If you come in dead on, you could still shorten it, retiller, and drop the weight.
Lastly, December until now isn't very long for that osage to dry out. You're experiencing that in the form of twisting. Rough out the bow, get it floor tillered, and then seal it with shellac, lacquer, etc. Give it some time to fully dry and then tiller your bow out.
Hope that helps. Just my humble opinion.