I'd like to use a couple of illustrations from some Novelty Press comics (1941-45 era) for a book chapter I'm contributing to a forthcoming anthology on World War II comic books. The publisher (in fact, most publishers these days) want either a signed release from the copyright holder or (in this case), some verification that the source comics are in the public domain. Even though I'm pretty darn sure Novelty Press titles are PD (they're available here, for example, and full stories have been reprinted in books like the "Spacehawk" book), I would like to lay out the steps I took to verify this.
I'm certainly not asking for anyone to DO this for me, but if you can direct me to the proper sources, I'll do the legwork myself. The Stanford Copyright Renewal database only does Class A (books), and the Copyright Office site refers you to Archive.org for pre-1978 material, but once I get there, I'd appreciate a hint as to where to start.
Thanks in advance!