73 340 oil pump

No, no, no... don't use abrasive inside the pump to smooth things out! That will just open up the internal clearances and the pump flow/pressure will drop like a rock! Just replace it... they are not expensive.

A squeal would be more likely a belt or pump. A squeal from the oiled internal parts of the engine pretty much means a badly damaged bearing or other part seizing up, and should not be run anymore without finding and correcting. I doubt that replacing the oil pump will fix an oiled part of the engine that is actually squealing.