You would need a 69# @ 28" to be spined 54# @ 31" Eddie. Natural taper of cane/boo arrows will account for the need of a 10-15# lighter spined arrow for that width handle.
So, if you make your arrows 32" long, w/125gr point, 70-75# spine should get you in the ball park if my math is right. Art
PS Just read Mark's reply, and if what he says is correct, try either Tonkin or the Japanese boo to get the higher spine.