It's hard to suggest a maker from the pictures you included, but the entire rifle might be a Leman product.
I don't know how you determined the maker, but unfortunately, it's not a Dickert & Gill. Your rifle is an original percussion gun, and both Jacob Dickert and James Gill were dead before percussion guns were being made.
None the less, it's a good looking rifle in what looks like very good original condition! If it were mine, I'd just put a good coat of cabinet wax on it and call it good.
John