Just wanna clarify on the UK comics a bit. They followed the TV designs about as much as the NOW books, but went a step further and incorporated some of the TOY designs into the stories. Specifically, the Super Fright Features suits, a few ghosts, Ecto-3, Ecto-500 and the design of Ecto-2 (minus the propeller trigger).
There were also two Slimer spin-offs produced by the companies who did RGB. The NOW version was all original until the later half of its run when it started reprinting the UK stories, and the UK book featured very little original content reprinting mostly stuff from the NOW series.
There was a lot of exchanging going on between the two books, both in stories and even covers. All of this is explained and evident when I get the Comicguide back up on its feet, hopefully soon.