so, now that my dad has seen my bow he wants me to make him one for christmas.  He shoots a compound now and wants to switch.  The issue is that his draw length is dang near 31", and it has to pull between 50-60 lbs.  He also wants it to be contrasted in color, so osage or something with a white back, or white wood with a dark backing, and so on.  My questions are
how long do i have to make a bow in flat bow design to acomadate such a long draw
and do i have to use a very strong wood like osage (which i have never used befor), or can i use hickory or oak and back it with....to get the dark contrast.
I would rather not use a stain.
let me know your thoughts please  
if flat bow is not the best option i am open to suggestion.