As to the people you listed who contributed, what would you expect? Birds of a feather flock together!
I was looking at an online summary of the book on Namebase, which is a site one of the contributors to that book (Peter Dale Scott) is associated with. I collect books on JFK and I have about 50 but not that one--should probably add it to my collection, LOL. It looks like Signet published it in paperback, so there should be some copies floating around. I've seen it around here and there at libraries and used bookstores.