Not to sound like a broken record, but characters don't have copyrights, because they're not "fixed works." The stories in which they appear carry the copyrights, and you can't legally derive from copyrighted works. (And you also can't step on someone's trademark.)
There are exceptions. The courts once ruled that Sam Spade, I believe, wasn't important enough to his own stories for his character to be covered under the books' copyrights. He was, essentially, a "stock" hard-boiled detective with a cool name. But otherwise, it helps to think in terms of the story, rather than the character.
MLJ didn't renew copyrights until after most of the Golden Age superhero stories expired, so you should be able to derive (adapt, change, continue) the stories to your heart's content, as long as you don't break any valid copyrights or violate a standing trademark. For example, you can't group the heroes on a team that looks just like the later Archie-published versions, and you definitely can't call them the Mighty Crusaders, because that would step on the copyright of the '80s stories. You also can't publish a Shield series or with the Shield as the cover's selling point, because DC probably has a trademark for those purposes, and it would look like you're trying to steal customers from them by creating a product only they have permission to produce. (Or maybe it'd be Marvel, given the name.)
And as mentioned, check with a real lawyer if it's important. "Some dude on the Internet said it'd be OK" is only worth mentioning in court if you want to see the prosecuting attorney's hysterical laughter...