He never got to introduce the Outsiders and Devastators, though. At least not officially, and not at DC. Cockrum left DC for Marvel around 1974, where he co-created a group called the "All-New, All-Different X-Men". Some of his designs for Legion-spinoff characters appeared over at Marvel.
We know about Nightcrawler and Reflecto. Power Boy looks like a guy with "atomic fists" or something. Trio is in all likelihood a Carggite, though from the drawing I can't tell if she's supposed to be black or not. Quetzal would be the winged woman, whose name evokes the Mexican (Mayan? Aztec?) flying god Quetzalcoatl. That leaves Typhoon as the generic-looking guy with the early 70's Cockrum-ish costume.
According to the X-Men Anniversary Magazine (Sept. 1993), "The wholly unique Nightcrawler wasn't even concieved as an X-Man, he was meant to be in DC Comics' Legion of Super-Heroes and, later, of a Legion offshoot called "The Outsiders". But according to artist Dave Cockrum, DC editor Murray Boltinoff felt the character was too funny looking. Cockrum eventually placed his pointy-eared, blue-skinned swashbuckler into [writer] Len Wein's all-international X-Men!"
For the development of Storm, there's a picture in that magazine of a proto-Storm character named the Black Cat, a shapeshifter. "Storm is perhaps the best example of how a character's look develops from creative conception to creative result. In the early 1970's, Dave Cockrum had hoped to create a new super-group for use in DC's Legion of Super-Heroes. Before that happened, he moved to Marvel and the X-Men project. For the new X-Men, Wein and [editor Roy] Thomas had conceived of a male X-Man with the power to maniuplate weather. Cockrum had already designed an alluring female named Quetzal, but everyone thought Dave's design for an African-American shape shifter named the Black Cat better fit the X-look, so the took the Black Cat's powers, and Quetzal's beautiful features, and combined them into Storm. The white hair was one of Dave's last-minute inspirations (just as long as it doesn't make her look like somebody's grandmother, warned Wein), and the cloak was a holdover from the go-go Marvel Girl design. Nothing creative ever goes to waste."
Tyr became a Legion solo villain. Wolverine looks like he became the Imperial Guardsman Fang (who was a Timber Wolf analog). Don't recognize the others. Looks like Belladonna (in the center, with the whip) would have been the leader of the group.
I got this picture from an ebay auction in December 2000, put up by Cockrum himself. I don't have any other info about the group.