I've got a shot at one that is outside of my comfort zone.....
It's a 639, round trigger guard, excellent condition. I think it can be had for around $300-400. (Maybe less)
How much difference for the fixed sight version?
I'm sure it isn't one of these, but just out of curiosity, what about the real early large extractor?

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Dean
SWCA #680 SWHF #446