The two books you mention were published in '51 and '60, respectively, which means there's no way they're in PD pretty much anywhere. This all by itself suggests that the site is probably
not legit.
From looking the site itself a bit further, it looks to me like it's a file sharing site that makes no attempt to police what files are shared, which means that most of its content is not likely to be legit.
Just a note, I'm going to "XXX" the name of the site, since we try to avoid linking or even looking like we're linking to such sites. You had to name the place to ask about it, of course, but now that we've got an answer, we really need to not leave it lying about for due-diligence reasons. I just didn't want you to wonder why it changed.
