all my letters to Laurence Roberts bounced ........
Castle of the Otter first showed up as a reviewers goof -- he thought that the fourth book of the book of the New Sun was so titled. Wolfe then wrote it anyway -- the subtitle is 'a book about the Book of the New Sun'. It contains essays, history, some background, and even one chapter where all the main characters (who were willing) stand up and tell a joke. If you liked Book of the New Sun, you'll probably enjoy it. It's available from the Science Fiction Book Club.
Plan[e]t Engineering is NOT reprints from Plant Engineering (by the way, Wolfe is now writing full time .) It was published by NESFA press, and may still be available from them. It commemorates Wolfes appearence as Boscone XXI GoH. The stories , articles and poems were chosen by a jury of NESFA members. It includes 'Books in the Book of the New Sun' and 'The Computer Iterates the Greater Trumps' as well as stories and , oh yes, one article from Plant Engineering on 'The Anatomy of a Robot' . I enjoyed the collection. If you too enjoy Wolfe, I can reasonably safely say you will too. Good luck getting ahold of it.
I read the Ziesing edition of Free Live Free and liked it. If such things bother you, it's really only borderline sf. I haven't read the Tor edition, but A Change of Hobbit has it as does Mark Ziesing Booksellers (P.O.Box 806 Willimantic CT. 06226).
Enjoy,