Have you ever read *The Letters of J. R. R. Tolkien *(ISBN 0-618-05699-8) edited by Tolkien’s biographer Humphrey Carpenter assisted by Christopher Tolkien.
I almost wasn’t going to post, as I figured this book is very visible and you’d probably already read it. But in many letters he goes into detail about his Catholicism. I was very edified to read how deeply religious (and staunchly Catholic) he was. There is a letter where he actually admits that he considered the Lord of the Rings a very “Catholic” work. I assume most people only peruse a book of “letters” but if you dig in and get dirty, you’ll be rewarded (I think).
I may write the book you’re asking about someday. I have studied the books from a Catholic point of view. Though Tolkien avoided “allegory” preferring to write a story with a history, there are clearly “allegorical” moments in Tolkien that are only best explained and understood from a Catholic stand point. If you ever want to share Tolkien/Catholic theories, just post.