I'd just drill a couple ½" holes in the bucket edge and bolt your pulley to that lip.
What you have conjured up is pretty flimsy (need clamps that fit) and cannot be trusted for whatever you want to lift, nor for whatever is below it (when) the item 'drops'. /forums/images/graemlins/tongue.gif
The idea is good, and it should give you some good steady control of your lift task. /forums/images/graemlins/wink.gif
Another way, using the clamps and no holes, would be to bolt two heavy pieces of angle iron into a number "7", and hook the "7" over the bucket lip (edge) and place the clamp on the top holding the piece in the bucket tight to the bucket. Then place the axle of the pulley (it too looks too lightweight) through the bottom leg of the "7" (will need two of these to make it work like you have it shown). And you will still need clamps that fit the thickness you want to clamp.