This collection is from the 53rd printing in 1960. The books will be shipped in two boxes (total weight is about 70 lbs.). The original volume 36 is missing, but I am including one from a 1910 edition (green hardcover).
Various is the correct author for any book with multiple unknown authors, and is acceptable for books with multiple known authors, especially if not all are known or the list is very long (over 50).
If an editor is known, however, Various is not necessary. List the name of the editor as the primary author (with role "editor"). Contributing authors' names follow it.
Note: WorldCat is an excellent resource for finding author information and contents of anthologies.