Pictures of the doublr in its entirety and any other marks would be of benefit. Your guess of the date is probably pretty close. As the the maker, not likely you'll ever know. The "ELG" in the oval denotes Belgian proof and manufacture. "JC" might be the inspector.
Whoever took a wire brush to it should absolutely cease and desist. I hope they went no farther. Ordinarily those don't have a lot of value as it is and to " clean them up" takes away what little they have.
As Sharps has pointed out the gun was made and proofed in Belgium. The Inspector's mark is a crown over the letter Y, This dates the piece from mid 1850's to the mid 1870's when the inspector's mark was changed to a star over a letter.