I believe the copyrights on the MLJ comic issues have lapsed; but, they maintained the trademarks on the names and characters, with a few exceptions, like Joe Simon's Fly and Lancelot Strong.  So, I wouldn't want to test them on the superheroes, no matter what.  The point i pretty moot, as they always seem to come off as more derivative, with every revival.  Even though Shield predates Captain America, Simon & Kirby made Cap way more popular and Marvel reinforced that.  You can point to similar problems with the rest of their characters.  I always liked them, but more in their pulpier aspects, from the MLJ years.  That's why I was way more interested in the Spectrum attempt than any other; but Archie wasn't willing to go there and still seems squeamish about that, even with what DC did with the Red Circle experiment (which wasn't especially edgy, but a bit more adult than Impact, 80s Red Circle or the camp revamp).