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Here is a comparison I did years ago between the two different models
https://www.milsurps.com/showthread.php?t=56864

And on this thread I have a photo of what I believe to be a M1904 Carbine...

As far as I am aware there isn't really any information you can really get off the serial number for these rifles (I have both a 1904 and a 1904/39). I know I tried finding some information years ago...

What are you trying to decipher?