I spoke with a local friend who's currently the ITC historian about the SS '60's. He personally helped with restoration on one of them...
"About the Stainless '60s. Allegheny Ludlum produced 2 of these at the end of the '60 production run. They knew that the stainless steel was much harder and more likely to damage or wear out the molds. One was supposed to have been stored in a time vault. The other spent quite a bit of time touring the country advancing the benefits of stainless steel. In the end it was quite worn out and really needed a restoration. Members of the VTCI did so in the early 80's and it made its debut at the 1983 VTCI Eastern Regionals in Niagara Falls along with another stainless '66 Lincoln Continental convertible. The '60 needed everything but, of course, was rust free. It was the only car that had its finish buffed with steel wool! It still exists and is owned by Allegheny Ludlum.