I am getting in on this discussion pretty late, but here is my take on the barrel.
I believe it is most likely a Super Grade barrel that slipped through the cracks, and was installed on a standard rifle. The "SUPER" stamp look's correct to me for a late S/G rifle. That said, all S/G Fwts barrels were rust blued, which this one does not appear to be. The only reason they were stamped SUPER was to earmark them for rust bluing. There is no other difference between the 2 barrels other than the finish. The date stamp is not a big deal in that Winchester quit stamping dates in 1956. Since the Fwt S/G was released in '55, there were not many with date stamps, if any at all. I have one of mine that is in the 1955 production, and it is stamped with a "55". My othr 3 are later guns made after 55 and none have a date code. I do not recall reading in the post what the s/n was or manuf date, but bet it was 56 or later. In conclusion I believe the barrel was originally earmarked for the Super Grade, but received a conventional Dulite blue and was installed on the standard Fwt rifle. The proofmarks line up very well, also indicating to me it is the original barrel installed at factory.
Just my thoughts.
Steve
