“Does the serial number look normal or does the “7” look etched in?”
it looks to me like a watchmaker spilled some oil in that area at one point, and it seeped into the seven, and accumulated dirt, and got darker.
There would be no reason for anyone to fabricate a serial number for a watch that isn’t super rare, whose value is not predicated on a production date range.
The minutia of serial numbers and date ranges that people obsess over when it comes to a Rolex Submariner or a Speedmaster do not apply to a 1950s-1960s Seamaster.
as for the black dial, I am no expert, but I will say I worked in a watch repair shop in the 90s, when smaller vintage watches were all the rage, and getting a watch refinished with a black dial was a very popular thing to do.
That said, yours looks pretty original.