Not sure how you folks from the northern part of the South build boats, but you sure make it sound complicated to change a few dimensions.
Most of the old boat builders I know would take some scrap plywood and cut out a couple of jigs. The jigs are shaped like a trapezoid with the side angles corresponding to the amount of flare or side angle you wanted in the boat at the point where you put the jigs. Then you attach the sides to the stem piece and wrap them around the jigs. Clamp the sides to the other stem piece (or transom if you're not building a pirogue). You've now got the overall shape of the boat, moving the jigs up or down will change the width and move the ends up as it gets wider and down as it gets narrower. Get it where it's pleasing to the eyes, put in the ribs, knock out the jigs and install the bottom.