I'm glad you found the answers here useful.
It occurs to me that, if you're in any doubt about the legality of what you are planning, you could always ask the Univ. of Illinois for their permission to convert their 1956 edition into an ebook. If it's out of print, and if they have no plans to publish it as an ebook themselves, they might just give you the OK. Just a thought.
In any case, good luck with this project.