OP;

Are you sure about that first "digit" or letter of the serial number? My 19-3 serial number starts with a number 9 K followed by 5 numerical digits. Mine shipped circa 1976. I am not where I can review SCSW 4th at this time but I was not aware that the 19-3 had a letter like S prefix to the K 5 digits.

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Charlie B
SWCA#3083, SWHF#570