Hi Richard..!
The MAG could be the correct type, as there were two variations of your type of MAG used. Can you tell me - does yours have the LWaA and the serial number of your "1936"? Photos would really help - especially of the top right side of the MAG.
As well -
no, the top of the mag should not be "ground down" in the middle..??
Best to you!
John D.