I'm a novice, but that short of a bow will require every bit of working limb available. Do you plan on a bending handle? Also, I believe that standard strengths of materials will tell you that you will get 3x more strength from the thickness of a limb, and not the width. I would guess that others may tell you 1.25" width on thicker belly, but I'm only guessing.
I'm really interested in the final outcome of this bow, so please keep everyone informed. This sounds a lot like a Chet Stevenson hunting weight bow. Can't weight to see it. (pun intended).
Good luck, Joe