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These are meant for a Sig P238 and P938. We do not have the exact specifications for the dovetails used on these handguns. You would need to contact Sig Sauer directly for the schematics on the slides.
I agree with the first answer; contact Sig Sauer customer service. BUT... Just for info: I read earlier today in a P238 review that when Colt came out with the Mustang, it was an early hit, but faded, and Colt quit making it. They subsequently sold the plans and specs and such to Sig, who made some adjustments, and released the P238. I have also read that Mustang mags will work in the SIG. My point is that there may well be a P238 rear sight to work in your 'Stang, due to the shared lineage and close resemblance. I think it's worth continuing to pursue, and I wish you good luck.