mattia ,
Stampings interest me , so I have been looking at your thread to see if I can tell you anything I might notice (of which yesterday , I was looking at your unit number stamp again and it perplexes me. But we can get into that later.
First off , you (I/anyone viewing) need to know what we are comparing specifically (apple to apples ..etc.) .
What MY (model year) case is the third photo (the 911/83 stamp with the round head 3) .... 73 , 74 , 75 , or 76 ?? I could be completely wrong , but isn't the normal small 3 digit stamp tool font for 1973 MY type stamp a flat top 3 ? Similar to the motor unit number stamp flat top 3 ...only small. Is this correct / anyone ? I will ask someone I know to post a 73.
I do not know which small 3 was used in 74 , 75 , 76 MY . If anyone has any photos of any of these , maybe they could post
And what MY case is the 2nd photo (the clean stamped 911/53).... 72 , or 73 ??
As far as your number being changed from a 911/53 to a 911/83. If that was the case...why would the 3 be restamped...as it would already be there ?
Lastly take a close/clear photo of the casting date mark and post it. It might tell us something. This is it , circled in the photo :
