When I built my first SOF, I tried to use Morris' rib gauge method and found it to be completely useless. I ended up clamping the keelson in place with spacer blocks on the deck beams to create the shape I wanted, then bent the ribs to fit. I did the same thing on my second and third boat. It just seems more sensible to me to define the hull shape - or at least the rocker - first, then install ribs to support that shape.