The top wing having that leading point for one, and the torpedo pod shape seem to be the biggest departures. Also, have you ever seen FractalSponge's version? It has a lot of detail. But as far as detailing goes, since it is a Cygnus ship, I'd take hints from the Lambda shuttle when it comes to greebles, to have more manufacturer continuity.
If you need any ideas for the rear end of the ship, one thing that occurred to me is that the rears of the torpedo pods would probably have to open for loading, like submarine tubes, unless they are loaded like a muzzle loading musket from the front. But I think being able to style them with a hatch on the rear end would add some character.