The Mighty Atom and the Pixies #6 (continued the Pixies series)
Mighty Atom #1 and Mighty Atom #3 from the 1957 series now in FTP. The latter two are reprints of Pixies 4 and MA&tP #6.
Whether the #6 should go into the Pixies folder or not I leave up to you. If not it should probably be identified as not be in the same series as 1 and 3. That series only had 3 issues.