2 Answers

Most of the books that I found written by Thornton Wilder were in fact, leather bound and wrapped in cardboard.

It is very difficult to find the illustrator for a book when you don't know who the publisher is.  Quite often the art that is used on the cover of any book is consigned by the publishing company.

To find any artist by intials alone is quite an impossible task as an artist that is not well known will not show up in any archives.  Even though this illustrator was most probably American that is not a "For Sure".  Also if this artist was a commercial artist then the likelihood of ever finding out who this artist was is practically nil.

The place where I would start if I were you would be with the publishing house if it still exists.

You may work with illustrator images by using of illustrator file recovery tool

Learn next writing http://www.oemailrecovery.com/illustrator_recovery.html