A few minutes with a flap wheel on an angle grinder will solve the clearance problem on the current pump. (or maybe using a thicker gasket?) There's nothing particularly "precision" about spinning an impeller around inside a coolant passage.
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!