I am now looking at the original problem with the water pump pulley. I offer these opinions for what they are worth.

The original problem was caused by the sidewall flexing under load, this lead to the aluminum work hardening and getting brittle. Shortening the sidewall increased the rigidity of the sidewall. The forces are now concentrated more on the inside radius, this radius should be bigger, as big as possible and free from machining marks as much as possible.

Aluminum is not good at taking loads like this and ideally it should be steel, failing that the radius must be bigger in the aluminum. A thicker sidewall with counterbores for the existing screws or longer screws would be much better as well.