I'd guess that the Belgian craftsman who had the trademark of an encircled H over 2 vertical lines sourced the longarm in the white or a tubeset from Auguste Francotte. Also that same craftsman could be the owner of the encircled Stamped Iron trademark on the standing breech. The initials RM may be that of the barrel knitter. Interesting rectangular crossbolt.

Kind Regards,

Raimey
rse