After bringing the pic into a view, the assembly number is "98" and the 2 letters "J" & "R" may be spangled. There will be an inspector's mark on the tubes. Also there looks to be a "L" about an inch forward of the "JR" on both tubes or it may just be my eyes. I'd guess the "London" somehow indicates the type of pattern welded tubes. If you find any initials you might make some headway on PeteM's site: http://damascus-barrels.com/Belgian_Trade_Marks.html

Kind Regards,

Raimey
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