I know creepypasta is fiction, that's why I apologized for the source. But the transcript there is real, and nothing else came up on a quick google.

The recording is legitimate. Here it is on archive.org, where I listened to it: https://archive.org/details/ptc1978-11-18.flac16

Following references on Wikipedia (which would have been a better way for me to find a reference in the first place), here's a site on SDSU with the tape and several transcripts, one by the FBI:

https://jonestown.sdsu.edu/?page_id=29084