Pretty sure I see prefix BEF in the photo of the yoke cutout, which correlates to the summer of 1989.

The bottom of the grip frame appears to have a factory SN format, just 40 years or so too early. Another thought, does there appear to be any welding evidence in that area? I suppose you could detach and weld the bottom of an N frame, then reshape it to a K; the question from there would be why.

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Alan
SWCA LM 2023, SWHF 220