I inserted a small card with numbers ranging from one to eight inside the cover of each of the remaining books. These were randomized and I had no knowledge of which book contained which number until just now.
Book number four is....
A History Of The World In 10 1/2 Chapters by Julian Barnes. Recommended by Trask.
I'll continue to do this until I've read all the books on the list. I may choose to insert one of my own from time to time (see Steve Martin) but I hope to complete all eight before too many months conclude.