The blower wheel nut is the hardest part to remove. You have to place a wrench on the pulley side to hold the motor from turning. Then with a 10mm socket on the blower wheel nut, remove the nut on the blower wheel.
NOTE!!!! This nut has reverse threads so you must turn in the direction as if you were going to tighten the nut to loosen it.
Since you found the spring on the old motor, you wouldn't have been able to reattach it to the motor because one of the tabs that holds the spring is broken off.