Andrew Birkett's nobugs.org
The only real issue with the casting is these three pockets, presumably bubbles caused by steam from the moulding sand.
Now, if I’d told you that I’d meant to make these holes (to save weight) you’d probably have believed me.
By some flukey coincidence, there are three similiarly sized bubbles around the central collar. Hopefully this means that the center of mass will still be roughly in the center, and the pulley will be balanced.