For an unbacked, narrow handle, American Flatbow design in osage I would use the following formula to determine nock-to-nock length:
(2 x draw length) + 10% = 56" + 5.6 or 62" when rounded up.
That's a good place to start from, go with 1 1/2" wide at the fadeouts and start tapering your limbs for the last 1/3 of the limb. You can go to a narrower limb, say 1 3/8 or 1 1/4 by adding a couple inches to the limbs...like 66 or so. A longer bow seems to be more forgiving to shoot, especially at longer distances. Something to think about.
For a bendy handle, just double your drawlength.