Take a look at the bluing on the SC6. I believe this is why Ruger chromed/nickeled about 100 of these in the mid 60's. This one's SN is about 500 off from my factory nickeled SC6. It's almost worth buying for the conversation piece although it has been converted.
http://www.gunauction.com/buy/11501747/revolvers-for-sale/ruger-old-model-super-single-six-2c-single-action-2c-sa-revolver-2c-.22lr
http://www.gunauction.com/buy/11501747/revolvers-for-sale/ruger-old-model-super-single-six-2c-single-action-2c-sa-revolver-2c-.22lr