Son in law just picked up a SP101 with the "bobbed" hammer, double action only. Could the hammer be swapped to allow single action option, or are there internal differences you can't see?
Im pretty sure you can buy a standard spurred replacement hammer and swap them out. Look on youtube for a video that shows you how to disassemble the SP101 and replace the hammer.
I'vr ordered parts for my Rugers and they sent them to me free of charge.
They didn't even tell me that if I did it I would void my warranty.
I have had them tell me no in the past but they don't seem to care now. I even got a birdshead rear frame for my Super Single Six (.32 H&R Mag) so I could change the looks to what I wanted and have something unique since they put those sorts of rears on shorter barrels and mine has a four inch bbl.
This was last year FYI so perhaps you can give it another try.
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As for the OP, this should be straight forward, switch the hammers and you should have what you want.