My copies of Gocky Club vols. 19 and 20 arrived today from SMJ.
Volume 19, "Groundwork of Variety", features random pieces of conte from series that Gotoh has worked on, including Blood+, School Rumble 2, Nana, Aria etc. Also included is a fold-out colour poster of Éclair (2nd TV version) and B+W sketches of Éclair (1st TV version), Cocoon, and Ucchii. There's a page with a block of text that mentions K-G.2 (as 『キヂィ２』), Gigantic Formula and Gemini Knives, along with an illustration I've not identified yet. The final section has a bunch of settei, that look like Gotoh original designs, under the titles 『ラビィ☆ディテクティブ』 (Rabbie Detective, a game I believe) and 『いきなり はっぴぃベル』 ("Ikinari: Happy Bell", definitely a game; cannot get the makers site, Terios, up at the moment but it's on gamefaqs.)
Volume 20, "Shadow Case Design Works", has rough versions of a number of Gotoh's illustrations, many of which were in Kinetic Girls.
I hope to have a few scans, from volume 19 in particular, up online soon.
Got one image up. Took a long time to get it to stick cleanly (I can never get two half of an image to scan at exactly the same angle and it takes forever to line them up properly, at least with Photoshop Elements). Not finished touching it up yet as fold lines are something else I'm not very good at fixing. You're also going to have to live with that blurry bit near the spine as I'm not going to flatten the book any more than I already have without a backup copy.
Now got that B&W drawing of Cocoon: