Hi Marc,
could you spare a moment to go through how you split up the dimensions of this bow? As in, upper/lower limb, height above center of the arrow pass, that sort of thing.
On backing twisted wood: if the backing is sound, you can use pretty much any grained wood you like. I used to agonise over picking just the right board for bamboo backing, and discovered years later, to my delight, that I could use highly figured, twisted and knotted wood...saving myself lots of time in the timber shop and making more interesting looking bows.
Dave