I've made several "board" bows from hickory. If you've got a piece with fairly straight grain, it is remarkably tough. I've made bows with pretty severe grain violations on the back that have held really nicely. With as short as you are looking to go, I'd get good straight grain, though. I'd stick with a shortened draw length. 27" sounds like an awful lot for a 48" bow, unbacked, even if it is hickory. It'll help to minimize the set, also. I bet 25 could go if you tiller it great!
Good luck.