Tom, The bowyer is in charge of the final draw weight,....within limits anyway. The overall design and the wood will place limits. Exceeding the limits will result in a broken bow or a suboptimal bow due to excessive set. I know many of the bowyers on this website enjoy making short bows, but I would tend to make a bow at least 66" long or bend-in-the-handle to accomodate a 28" draw. Some factors that increase the stress on the wood (and thus increase chances of breaking) are; shorter working limbs, narrower limbs, longer draw length and increasing draw weights.
I have made a limited number of yew bows, but I would think that a 60# bow is do able from a 64" stave. I would make the bow slightly wider than I would for a longer bow, and would would tiller the bow to bend slightly in the handle.
The whole issue of design /draw weight / tillering is discussed in most bow building texts, especially in the Bowyer's Bible series.
Most bowyers find that their first bow ( or 2 or 3) either break or are markedly lower draw weight than hoped for by the time the tiller is correct. There are many woods that are cheaper and easier to get than yew and if this stave is special to you, i would suggest getting a cheaper stave and making at least one successful bow before starting on yew. Ron