Some points to ponder...
Ruger did show a 6-1/2" prototype of a .32 Mag. stainless steel Single-Six on one of their tradeshow displays about 1991.
Second...I'm not sure I would go by what Ruger says the gun was shipped as. We've had too many guns (unusual ones) come through here with box markings different than what the gun actually is inside. If Ruger didn't catalog a KSSM4, why would they ship it as a KSSM4?
Had a SP101 here once that was shipped as model KSP-240 (.22 LR), but lo and behold that thing had a factory applied .22 R.F. Mag. rollmark on the barrel lug! .22 Mags in the SP101 were never offered commercially, and it is a mystery how many were really produced....but all prototype and pre-production only....and all shipped through normal distribution as .22 LR.
Also got into a batch of "D" guns from a distributor once, 21 in all. 7 of them either were the wrong model inside the box (as listed on the end label) or weren't even marked with a "D". Two of those were Bearcats and had the "crow's foot" "used" stamping as a prefix to the sn! Found out later these were really supposed to be "D" stamped, but......
I would do the ole' magnet test on that stainless .32. Stainless will attract a magnet, but not as heavily as a blued steel Ruger.
Be sure to let us know the results! If it is stainless, then I would want to hear more about that gun for the reference!! It would definitely need to be documented!!!
Just as a sidenote, does the sn tell you the gun was made about 1991 or so???
Its just too tough for me to discount anything from only a picture. Seen and held too many things that shouldn't exist.
Chet15