I think this is probably a question for LDC. :-)

Actually, I think you need a real lawyer for this one. Yes, the copyright should have expired under the original act, but the Sonny Bono extension or DMCA may have extended it. If the book is published by a company that still exists, it is they who will enforce the copyright, if any, so look for the publisher. If you do assume that the work is out of copyright and use it, all that is likely to happen is that the present rights owner may ask that we remove it, and we will have to do so (assuming the copyright is in fact valid). Last month I would have added "it's not like anyone ever presses criminal charges for copyright violation...", but that was before Sklyarov.