I haven't been following the whole thread but checking in once in a while. It's a pretty interesting project you've taken on.

You could gain some mechanical advantage by going with multiple reaving with your pulleys. Put double pulleys where you have the singles now, then mount singles closer to the winch. Run the cable from the winch through one side of the double sheave, then through to the single sheave and back through the other side of the double and out to your attachment point on the metal. This should reduce the amount of force you need to turn the crank on the winch.