The key factor here is the shape at the top of the frame boss, just behind the barrel. That frame came with a heavy barrel, not a tapered barrel. Given that a serial number of K208537 puts shipping in 1953, this gun could not have shipped as a .38 Combat Masterpiece. None of those, by that time, had lost the angle taper on the front frame boss, because they were all still shipping with a tapered barrel. Only the K-38 Masterpiece at this time would have the flat frame boss.
I can't speak to the origin of that barrel and sight arrangement. But I'm absolutely convinced of the frame model.

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Jack
SWCA #2475, SWHF #318