I'm just a bystander trying to understand. Now it seems that a person buys a short water pump for fan clearance to radiator?, and then adds a spacer to extend the fan out?
What? I suppose the answer might be they are buying the short pump to align V grooves, not for the fan. But no one has said that yet. I'm still waiting to hear why people are buying a short pump. Maybe they don't even know. But I envision a perfectly good motor with belts aligned and then someone buys a short pump and all hell breaks loose. So I assume they had a fan to rad clearance problem they thought they were fixing. I'm talking about folks that are NOT doing the adapter plate. The adapter plate is a totally separate issue, with some different goals, and can not be discussed at the same time.

Also as Jerry and others have cautioned! Do not "tweak", cut, or bend blades. This will cause vibration, out of balance, deflection and injury to parts and people.
We are talking high RPM's here. Slight modification to hub hole or mounting holes should be OK if strict care is taken to maintain concentricity and tight fit.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn