Another overheating situation 63 Slant six

When I bought my fairly well maintained 64 slant I went for my first drive, went less than a mile and the Temp gauge was pegged. Nursed it home and took out thermostat and did a drainage test on rad which seemed unplugged. Still overheated right away. Took the water pump off and found that the press fit plastic impeller was spinning on the shaft. Strange failure. I'm used to seal or bearing failure. So an apparently normal looking pump may have failed. Maybe you can take a heater hose off and look for flow? Obviously in your driveway at idle! Or speeding down the pike, your call!