1965 904 Real Seal: Can it be change in car?

Remove the driveshaft, at the flange. Remove the flange. Pop the seal out (might have to use a couple of sheet metal screws in the seal). Install the new seal with a driver, that has a hole in the center to clear the output shaft. Reinstall flange ant driveshaft. Word to the wise: the 65 seal is different then the 64 seal.