We need more info to help...find the engine casting number found just above the oil pan on the front right side of the block (may require a putty knife to clean out the recess it's found in). That will help us determine what decade your block was cast, date code D204 could be April 20th of 1944, 1954 or 1964.
Also, post a picture of the stamped serial number 0304213.
Mike B
