I don't care for the John Flynn method because of the long diagonal. It's hard to cut, hard to sew, and even harder to keep it from stretching.
Assuming a 3" extra all around (so the backing needs to be 62"x55") I would cut one length that is 62"xWOF, cut off selvages, and make the second piece 62"x whatever is needed to make the width 55". I really wouldn't expect to notice where the seams are on the back, but I would prefer that one not be too close to the edge of the finished quilt.
The exception to this would be if the quilt is going on a longarm. In that case the backing seam should run parallel to the rails. You might need to change the direction of the seams in that case, depending on the quilting design, and then I would definitely think about keeping that backing seam away from the edge of the top, which might require a different layout.