Some info per Atlas Tales.
Siefringer and Epp were part of Powell's studio providing inks and backgrounds and sometimes letters. Siefringer's name is displayed prominently on page 1, panel 2 and page 2, panel 1. Epp's on page 4, panel 3.
info per Atlas Tales.
Colan credit and story info per Michael J. Vassallo's blog:
http://timely-atlas-comics.blogspot.com/2011/08/gene-colan-1926-2011-timel…