Cut the filter open and see what sort of junk is in it. Bearing material would be obvious but it sounds like either the clearances were off or else there was junk in the oil galleys. Also pull apart the oil pump and see what the rotors look like. Who assembled the motor? They are responsible for the final cleanliness of all of the parts. Any oiling modifications on the motor? I knew a guy who put the copper tube in a small blocks oil galley for roller lifters and forgot to drill out the feed for the mains, wiped the crank out. Look for missing screw in and press in plugs in the galleys as well.