Information for this issue supplied by the Atlas/Timely discussion list.
First published work by John Buscema according to Back-Up #14 (edited by Tristan Lapoussière) (info via Stéphane Petit on the Error Tracker, January 2009).
No, it is not the first published art by John Buscema but it is his first professional art done.
The first published art is Lawbreakers always loose! #3 (Aug 1948).
These infos come from the John Buscema checklist built by Jim Vadeboncoeur Jr and Michel Maillot.