Hey Matt. In general, the problem with bendy handles is that they need to NOT be the weak link in the tiller chain. So the handle needs to be nearly as wide as the widest part of the bow or the same as. Its not practical to make a D-bow with, say, a 2" wide handle as its just hard to grab on to. So most D bows end up around 1.5" and that width limits what the bow can end up being.
I've never even heard of a 31" draw. Are you sure you understand how to measure it? That's a long draw for any size bow let alone a 57". Its possible for sure but to get that much bend from a short bow you have to have good quality wood and good tillering.