Some other guesses...
DC only: Mort Meskin; all the Batman guys: Kane, Moldoff, Paris, Sprang; Mike Sekowsky, Sid Greene, Pat Boyette, CC Beck.
Wayne Boring came to mind, but I remembered that he'd done a few issues of Captain Marvel.
Marvel types: Barry Smith? (He must have done something for DC, right?); Gary Friedrich; Larry Lieber; Dick Ayers.