Dump the butt blocks. Find someone who has built a Pygmy boat and use the method described in their assembly manual. It is described two places: the first is where they tell you how to butt the pieces together; the second is later on when you reinforce the butt joints just before glassing the inside of the hull. 4 oz tape can be found easily (if you are in Seattle its Fiberlay, if you are not in Seattle its fiberlay.com), mylar too. The advantage of their system is that the first joining doesn't create and unbendable a flat spot on the pieces. After the pieces are in the bent shape (hull all glued together and formed) the reinforcement is like the butt plates but it conforms to the curve of the hull.