The rear dovetail is cut as if it were a standard/26" barrel. SRC round barrels I have are cut much farther back. Front of the forearm is either broke or adjusted as well.
Q: Could you post a clear pic of the barrel address? Is the s.n. stamped on the underside of the barrel? If so, post a pic.
It just seems that if the factory pulled a half-oct barrel from inventory, cut to length that the rear dovetail would have been cut similar to other SRC's. If I was to guess from afar I'd say it was a cut half-oct barrel added. Get the letter and prove this theory wrong.