You want me to believe that a 257 Moki only makes 32 pounds of thrust? You must have something wrong here, these engines are swinging props in the 28 - 34 inch range. My guess would be that this engine easily makes 90 pounds of thrust. If the plans say use an engine in the range of 30 - 50 pounds, I think you still need to reframe the question.
The math is cross sectional drag aah never mind, here open this: