I have a WWII Remington A303 that my dad sporterized. Like most hunters, I have little interest in guns as a collectable item. They are a tool, and not worth much if you don't take them into the field. I'm no gunsmith, but don't hesitate to tinker with my guns if there is something within my capability. Do you have a photo of your Fusil de Chasse that you could email to me? It sounds like a neat project.
Somebody on rec.guns just posted a great site for finding out the date of manufacture of guns.
http://armscollectors.com/sn/winlookup.php. All the search links are in the frame on the left hand side of the screen. Scroll down.
I found out my Model 1912 was manufactured in 1913. All the blue is worn off where the pump slides, but there isn't a speck of rust on it and the barrel is still 98% blued. I wonder how I managed to haul it through so many duck and pheasant hunting trips in the 70s and 80s without doing more damage. I guess the habits my dad taught me really work. The day isn't over until the gun is clean.
It is amazing how durable a good gun can be if you take care of it.