The gun in question is pictured in a post on the DoubleGun BBS. The barrels are indeed acid-etched. Stockel mentions M N Colleye as being in business from 1850-1865, Im told.

The Manufacture Ligeoise stamps with the crown within the oval that I have seen pictures of are quite different in shape to the stamp on the barrels, but it might reflect an earlier version of their stamp. This might explain the low serial number.

My comfort zone is British pinfires. Im afraid Continental guns are outside my area of knowledge, so again, thank you all for your input.