Simmons provided barrels for the Ithaca SBT and Browning Superposed, Remington Model 32, and Krieghoff K32 in the 60s, but they were made by Cordy of Liege. In light of the Simmons Vent. Rib is seems possible that Simmons used Masquelier also.
Atlas Arms in Chicago offered replacement barrels for Smith and Parker guns using tubes made by Vickers (England) and fit and finished by Armaf in Belgium. These barrels have a 1954 proof date code.
AND these are replacement Smith barrels by Armi Sarezzo, also 1960. Barrels for Lefevers were also made by one of the Bernardellis of Brescia; handled by a firm in FL named Hardin and Knight