You're referring to pound-force (448 Newtons) rather than pound-mass (0.434 kg).
Pound -- from Eric Weisstein's World of Physics
To avoid the confusion between pound-mass and pound-force, maybe we should redo the calculation in metric units. I get the force on the pulley is 1986.85 Newtons, and the minimum rated load for the platform 202.53 kg, which is 467 lb (pound-mass) w/ rounding. The combined mass of the three stuntmen is 227.85 kg.