I was thinking British Service Revolver myself initially when looking at the photos, especially since that front sight at first glance resembles the Parker-Hale sights which were installed on some of the BSR conversions done in Britain, but then again, a British conversion to .32-20 would be a first for me
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The number will be stamped as Muley says, not pencilled, both if the stocks belong to a BSR or a US frame.