My guess is that "The former Methodist missionary" refers to Huston Smith.
Leary and Smith hung out together.
Huston Smith was raised Methodist.
Strange sources for Watchtower literature. Very strange.
https://en.wikipedia.org/wiki/Huston_Smith
Due to his connection with Heard and Huxley, Smith went on to meet Timothy Leary, Richard Alpert (Ram Dass), and others at the Center for Personality Research, where Leary was Research Professor. The group began experimenting with psychedelics and what Smith later called "empirical metaphysics."[7] The experience and history of the group are described in Smith's book Cleansing the Doors of Perception. During this period, Smith was also part of the Harvard Project, an attempt to raise spiritual awareness through entheogenic plants. During his tenure at Syracuse University, he was informed by leaders of the Onondaga tribe about the Native American religious traditions and practices, which resulted in an additional chapter in his book on the world's religions. In 1990 the Supreme Court ruled that the use of Peyote as a religious sacrament by Native Americans was not protected under the US Constitution. Smith took up the cause, as a noted religion scholar and, with his help in 1994, Congress passed the American Indian Religious Freedom Act Amendment, basically overturning the Supreme Court's decision.[8]
Smith is a practicing Christian who credits his faith to his missionary parents who had "instilled in me a Christianity that was able to withstand the dominating secular culture of modernity."[9]