Pictured here is an NOS A-6675 oil pan. This is the 1929-31 style engine oil pan with the round threaded drain plug bung.
Later style engine oil pans used a hex-shaped threaded bung rather than a round bung.
Ford began production usage of the hex-shaped oil pan drain plug bung on July 14, 1931, according to the Rouge engine production Foreman's original handwritten daily log books (at the Benson Ford Research Center).
The use of the hex-shaped bung plug continued on into 1932 and the production of the Model B engine oil pan.
Note the oil pan dipper tray without the later added drain holes.
Pictured above is a close up showing how the front seal reinforcement was spot welded to the pan and then the joint was tinned and soldered, and then finish machined to provide a precision fit for the grub seals shown below.