In hopes of answering both Ken and George (and realizing that there, again, aren't any bold-faced canonical ANSWERS), "rights" are funny things. DC owns the "rights" to Fawcett, Quality, and Charlton properties, among others, but since many (but not all) of the books are in the public domain and the trademarks aren't kept current, what do they really own?
Since you can't (so far, and in the United States...except under very limited circumstances involving foreign war heroes that don't really apply here), bring something back under copyright, then the only possibility remaining is trademark, plus whatever has not yet fallen into the public domain.
So in the Kubert case, Joe continues to hold a monopoly on the publishing rights to whatever was renewed. He (presumably) also owns the name and character design as his literal "mark of trade"--in other words, an assurance that all comic products sold as "Tor" come from him. (Again, that's the perpetual Disney problem--a cake with Donald Duck's face from a local bakery doesn't have Disney's quality assurance, so they must stomp them down.)
So, first and most obviously, you may not use anything that's under copyright, because the copyright owner has an (temporary) exclusivity agreement with the government. Second, anything that has fallen into the public domain can be used for any purpose, including resale. However, third, you may not use someone else's trademark as part of your "trade dress," because it implies association or endorsement.
So basically, yes, you can take an issue of Captain Marvel Adventures or Tor (assuming it's in the public domain), and as long as you don't step on anybody's trademark on the "sales features" (the cover, basically), there'd be nothing illegal about reprinting and selling it.
(And all that, of course, is with the caveat that I have no formal legal training. I don't even play a lawyer on TV.)