Red mulberry or white? I find them pretty different.
Red mulberry seems to want to pretend it is mediocre osage. I'd chase the ring and make a 54" bendy handle bow, not a pyramid. Should be ok at that draw and weight.
White mulberry wants to act like really good white wood. It can take some set, but loves heat treating, and sapwood and heartwood are both fine. Small logs and sapling staves usually have lumps on the front and a streak of heartwood on the belly. That could make you an ALMOST pyramid (crowned front), but you'll need to leave ti as wide as you can, make the handle tiny, fades abrupt, and a few stiff inches at the tips.