Nifty, but no clue here. Markings would indicate Khyber Pass to me as well. BUT, I am as far from an expert in odd and unusual pistols as you will find. Very cool, make a really neat wallhanger in a shadowbox.
Its a Belgium, probably 7 mm, pinfire revolver made before 1893 ( the ELG proofmark in an ovale was in use before that date )
You probably have a lettre with a crown or star above on the cilinder .... crown = before 1 january 1877 , a star = after january 1877.
The screw and ejector rod are missing