One thing I thought would be helpful is to link to the YouTube video described in the opening paragraph: https://www.youtube.com/watch?v=UMF-cyHAaSs
It's from a 1957 CBS documentary series called "Focus on Sanity" that featured interviews with Aldous Huxley and Gerald Heard, among others. I found it fascinating and my questions about it were actually one of the motive forces for why I wrote the book.
I believe the recording was first brought to public attention by Don Lattin, whose books The Harvard Psychedelic Club (2010) and Distilled Spirits (2012) are both great.