may I ask why the sinew backing. If you get a nice straight grain 1/4 sawn board 1 1/2 to 2 inches wide by 1 inch thick , taper the handle to the ends, it could easily give you a 60 lb bow. Also back with wood or hide, maybe. I would reseverve the sinew for a nice stave bow, raw cut from a tree.I have made 80 lb hickory bows from that demonsion, added a small board for th handle and shaped . Then added elk hide for backing for string follow, which was next to nothing. Good Luck Denny P.S>I for got the length is also very important. I have found board bows to be more stable at 66 inches or more. However with care you can get success with smaller.