Pretty sure Mark Larson can make the extension disappear. Looks to need a new pad anyway.
Nice gun. Fair warning, you will spend a lot of time looking for number one!
I would wager that you will find the barrel walls to have substantial thickness, it was typical on French guns. Low pressure is a good thing, but, takes on less urgency with a French double gun that has .050-.080 barrel walls, 9 inches from the breech.

Best,
Ted