The barrels are replacements by
Masquelier Lige. The
lettre annale is 1960.
http://www.littlegun.be/arme%20belge/artisans%20identifies%20ma/a%20masquelier%20gb.htm 
Simmons provided barrels for the Ithaca SBT and Browning Superposed, Remington 32 and Krieghoff K32 in the 60s, but they were made by Antoine Cordy of Liege. In light of the Simmons Vent. Rib is seems possible that Simmons used Masquelier also.
Steve Tasitritsis 'ATLAS ARMS', 2704 N Central, Chicago and (later) 7952 Waukegan Rd. Niles, Illinois offered replacement barrels for Smith and Parker guns in the 50s and 60s using tubes made by E.S.C. Vickers (England) and fit and finished by Armaf in Belgium
http://www.littlegun.be/arme%20belge/artisans%20identifies%20a/a%20armaf%20fr.htm 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
AND there are unmarked Parker barrels out there
Replacement: do you recall who made your Boehler barrels?
