The bolt pattern can be slotted with a rat tail file to match the holes in the water pump, but the center hole MUST be a close fit over the water pump hub to allow the fan to run concentric to the shaft. If the hole in the fan does not match the hub diameter DO NOT attempt to drill or file it out. Any runout at all of the fan center will set up a destructive harmonic vibration that can result in fan blades breaking off at the center. Ditto for bending or trimming the fan blades- - - - -JUST DON'T DO IT!

I've seen some very nasty sheet metal damage and severe injuries from thrown fan blades.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!