Interesting old S&W. Looks very nicely done. Would be fun to know who did the work. And yes, that is one of the Bowen target-type rear sights on your Ruger. Don't let it get away from you! 

Might as well add another example from this unknown gunsmith. There's a couple others on this board with modified guns from the same individual.
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Not necessarily unknown - information from David Carroll indicates that the gunsmith was Joe Lamping of Cincinnati, in the 1940s and '50s. Copy and paste from post #10, in this thread: http://smith-wessonforum.com/s-w-ha...s-w-1917-a.html?highlight=Cincinnati+gunsmith
"Looks similar to the hammer on a gun modified by Cincinnati gunsmith Joe Lamping. Here's some text and pictures from an old auction on Gunbroker by David Carroll (woodlawn boys):