The first four issues of this series contain material from a variety of sources, including freelance artists, pulp writers (some of whom were on staff with Martin Goodman's operation), Funnies, Inc., the Chesler shop and possibly the Iger shop). The bulk of issues #1-3 comes from the Chesler shop, with most of #4 probably coming from Funnies, Inc. Once the series relaunches with issue #5 and again with #6, the material is back to a mixture of Funnies, Inc. and the new but growing Marvel in-house staff.
(per conversations on the Timely-Atlas-Comics mailing list, August-September 2010)