I think you are right about the action, Larry. The front screw in the front wood appears to be a replacement. The barrels/action could have been sourced from Belguim, but, it was definitely proofed in St. Etienne, and it was post 1900.
I highly doubt the case is original to the gun. Cool case, cool gun, but, they simply don't belong together. 18.3, typical 12 gauge size from that part of the world, 65mm chambers. Does not appear to have been proofed in a finished state, likely a small gunmaker produced this one.
I'd invest in a strip and clean from someone like Kirk Merrington, and find out if it fit me and I shot it well. If I did, I'd use it.

Nice hunter shooter.

Best,
Ted