Lloyd, the incidence measurements you quote for the top wing and horizontal stab are about "right on" for a biplane. Top wing is positive so it will stall first. If the bottom wing were to stall first and the top wing was still flying you would suddenly have a tail heavy airplane! NOT GOOD! Positive in the horizontal stab helps keep the plane flying level with all the lift of the two Semi-symetrical wings.
Can't help you with the possible stamping mistake. Good luck. Always wanted a Great Lakes Trainer. Tom