I have put some more file on my flickr account with some pictures of the docking ring. Also another version of it. Feel free to use the solution. I'v borrowed quite a few from you.
The 57518 is in Dark Bluish gray. If you go to build it, make sure to use used parts that have some slack into them to get the cone shape of the docking ring.
I'm thinking of lower the exhaust port into the hull to get a lower profile, but that will be a later matter.
I have used this pictures as a template for my moc. Star Wars - Halcón Milenario 3