David Hyde has written/compiled a Philip K. Dick reference that astounded me. An Index to the Selected Letters of Philip K. Dick: 1974 was recently published and the book doesn’t only contain an index of topics and what letters they appear in. The reference work also includes a summary and discussion of the content of the letters written by David Hyde so if you don’t own a copy of the 1974 letters, you can still understand what Philip K. Dick wrote about and experienced in 1974, a pivotal year for Dick and for scholars.
The book is available now as a trade paperback or in Kindle format.