Finally got my Curlew in the water Still need a backrest and some deck rigging but I just couldn't wait any longer. Totally flat water but performed great.
I too inserted braces between the stem and stern and the strongback to keep them level until the lashing was complete.
I had no problems with my frames moving, I attached them to 10 inch lengths of 2 by 4 with 3 inch deck screws.