I believe that Tolkien is one of the folks he read Old Books with.
Tolkien is the one that convinced Lewis to leave atheism behind and become a Christian. Tolkien's poem "Mythopoeia" - https://en.wikipedia.org/wiki/Mythopoeia_(poem) - was instrumental in that process.
It's worthwhile to read it, but as a warning, it was written from one (highly educated) friend to another (highly educated friend), and it is not easy to understand what Tolkien is trying to say about the nature of reality without reading through it a few times: http://home.agh.edu.pl/~evermind/jrrtolkien/mythopoeia.htm
> All wishes are not idle
That line alone could tip me over to Christianity. I'll have to think more about this.