This is such an awesome illustration, and a very elaborate crossover between giant sized heroes and villains alike - thanks so much for doing this in the first place, and allowing us to feature it at our galleries!
I know now, and submitted many of the individual pieces to Kaijuden, as well as some miscellaneous groups I have ties to. And this is especially good, because our Super Robot gallery / folder could use some more love.
You know, if you want some suggestions for future entries into this Giants series of yours, I'll be more than happy to do so.
Really awesome live action take on the Super Robot genre, that for a brief time, was more popular than even its anime inspirations. The series is available on American DVD and some video-on-demand services, so it's very much worth checking out.
This series was a VERY loose remake (rip-off?) of "Johnny Sokko and His Flying Robot" from the same company Toei Production, with several episodes were heavily edited together to make the direct-to-video film "Brain 17" around the late 1980s here in America.
Here's two better assembled galleries featuring 1-7's enemies, the Roller Robot ([link]) and The Hurricane Robot([link]).
The Roller Robot might be the subject of an August / September art-jam here at Kaijuden.
King Joe from "Ultra Seven" and "Ultra Galaxy: Mega-Monster Battles" - [link]
Believed to be the very first giant robot in Japanese fiction to be made from multiple vehicles combing together (in this case, four alien spaceships), King Joe is a mechanical assassin and destroyer sent by the underhanded inhabitants of Planet Pedan. A more powerful, upgraded version dubbed King Joe Black appears as a recurring enemy in some of the more recent entries in the Ultraman franchise.
Far more helpful YouTube video featuring King Joe in action: [link]
Godzilla's one-time ally and attempt to bring in a Super Robot-like superhero in the franchise. And unlike Mechagodzilla, he's humanoid enough to work with your Giants series, despite being a rather wispy, slim character overall.
Talos from "Jason and the Argonauts" - [link] (scroll down)
The classic bronze giant / automaton of Greek mythology, made semi-famous through the Ray Harryhausen film from 1963. Unfortunately, if you were to do an illustration with your usual perspective looking up, we'd probably get an overt look at his metallic underwear.
Robot Randy from "Courage The Cowardly Dog" - [link]
This character is a little too obscure, but doesn't hurt mentioning regardless.
Of course you didn't do Talos, as no one wants to look up his metallic undies, if you're referring to the Harryhausen design of course.
Awesome to here that my suggestions were useful, and I'll be happy to make more if you so desire. I also saw that Captain America vs Nazi robot picture you did, and will be adding that to some groups soon, along with giving you a DA watch.