Where is the serial number on my transmission?

[turnjare]

Hi Everyone,
Question, where can I find the serial number in my transmission? My truck seems to have been pieced together over the years. The vin is a 1949 3600, the engene is a 1956 235, and the rear axle may be from 1949. (Not sure, it is stamped "FG 728", maybe "EG 728"). Anyway, I want to ID the transmission. I can find casting numbers pictured below, but where are the stamped numbers? Does anyone have a picture of where to find these? The manual says they are located "on rear if case, just below cover on left side", but I still don't know what I'm looking for.

Thanks in advance for any help!