I know we've had threads regarding the various outfits doing replacement barrels for the "time bomb" damascus vintage U.S. doubles in the 50s - 60s; both here and the PGCA forum.
The threads I found were mostly missing images however, and some that I saved were low resolution.

The major mover was Steve Tasitritsis of "Atlas Arms", 2704 N. Central, Chicago then 7952 Waukegan Rd., Niles, Ill. The tubes were Vickers Steel and barrels fitted by ARMAF in Belgium
http://www.littlegun.be/arme%20belge/artisans%20identifies%20a/a%20armaf%20gb.htm

Semi-finished barrels were also supplied

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September 1963 Guns Magazine "Parker & L.C. Smith Barrels"

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Parker with the earliest date code I've seen; 1954

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AHE with 1961 replacement barrels

[Linked Image from photos.smugmug.com]

[Linked Image from photos.smugmug.com]

https://sites.google.com/a/damascusknowledge.com/www/home