"Best Fluid Steel" was just a generic term and does not establish the tube maker.
Ithaca NIDs were so marked, with tubes from Canons Delcour which was in business until about 1968 when they were acquired by Fabrique National de Herstal.
I've not seen "J. Cannon" - maybe Joseph Cap?
http://www.littlegun.be/arme%20belge/artisans%20identifies%20c/a%20cap%20joseph%20gb.htm

Demi-bloc is the method of joining the tubes to the breech and does not establish the maker
https://www.boxallandedmiston.co.uk/shotgun-anatomy/difference-between-a-demo-and-mono-bloc-barrel

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